OSX: Reasonably large number of directories causes "FSEventStreamStart: register_with_server: ERROR"

# Boot Bug Report

## Platform details

* Platform (macOS, Linux, Windows): Mac OSX
* Platform version: Sierra 10.12.6
* JRE/JDK version: "1.8.0_121"

## Boot details

```
BOOT_CLOJURE_NAME=org.clojure/clojure
BOOT_CLOJURE_VERSION=1.8.0
BOOT_VERSION=2.7.1
```

### `build.boot` content (if applicable)

```clojure
(set-env!
:resource-paths #{"resources"})
```

## Description

When there are a reasonably large number of directories in `resources`, running `boot`, even without any tasks, causes many errors to the tune of:

```
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2017-09-20 11:45 java[9766] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
```

More directories (eg. 3000) causes the task to never finish / error out.

```
Boot.main Boot.java: 257
...
boot.App.main App.java: 491
boot.App.runBoot App.java: 399
org.projectodd.shimdandy.impl.ClojureRuntimeShimImpl.invoke ClojureRuntimeShimImpl.java: 150
org.projectodd.shimdandy.impl.ClojureRuntimeShimImpl.invoke ClojureRuntimeShimImpl.java: 159
...
boot.main/-main main.clj: 206
boot.main/-main/fn main.clj: 206
...
boot.user/eval32 boot.user3887463377436593005.clj: 5
...
boot.core/set-env! core.clj: 873
...
clojure.core/swap! core.clj: 2253
clojure.core/swap! core.clj: 2263
...
boot.core/init!/fn core.clj: 776
boot.core/configure!* core.clj: 311
...
boot.core/fn core.clj: 797
boot.core/set-user-dirs! core.clj: 196
...
boot.core/watch-dirs core.clj: 744
...
org.projectodd.shimdandy.impl.ClojureRuntimeShimImpl.invoke ClojureRuntimeShimImpl.java: 117
org.projectodd.shimdandy.impl.ClojureRuntimeShimImpl.invoke ClojureRuntimeShimImpl.java: 124
...
boot.watcher/make-watcher watcher.clj: 125
boot.watcher/service watcher.clj: 94
boot.watcher/service/doreg watcher.clj: 93
boot.watcher/register-recursive watcher.clj: 65
boot.watcher/register-recursive watcher.clj: 62
boot.watcher/fn/G watcher.clj: 25
boot.watcher/fn watcher.clj: 52
com.barbarysoftware.watchservice.WatchableFile.register WatchableFile.java: 43
com.barbarysoftware.watchservice.WatchableFile.register WatchableFile.java: 34
com.barbarysoftware.watchservice.MacOSXListeningWatchService.register MacOSXListeningWatchService.java: 52
java.lang.Thread.start Thread.java: 714
java.lang.Thread.start0 Thread.java
java.lang.OutOfMemoryError: unable to create new native thread
clojure.lang.ExceptionInfo: unable to create new native thread
file: "/var/folders/dm/63qgv3gx0_96qkqbz6xpdzgh0000gn/T/boot.user3887463377436593005.clj"
```

## Steps to reproduce

```
cd resources
seq 600 | xargs mkdir
cd ..
boot
```