"Started task" urgency boost change seems to apply before "more urgent tasks" change, not after.

Example session:

```bash
$ task add test1 pri:M
Created task 1.

$ task add test2 pri:H
Created task 2.

$ task next

ID Age P Description Urg
2 6s H test2 6
1 9s M test1 3.9
```

Starting less urgent task, but not there is no warning!
**BUG: Here I would expect a "You have more urgent tasks." warning, but it's not shown.**
```bash
$ task 1 start
Starting task 1 'test1'.
Started 1 task.
```

Now M-priority task is more urgent because it's started:
```bash
$ task next
ID Active Age P Description Urg
1 6s 20s M test1 7.9
2 15s H test2 6
```

When trying to complete it, I do get a "You have more urgent tasks." warning even though the task was the most urgent.
**BUG: Here I would expect no warnings, but "You have more urgent tasks." warning is shown.**
```bash
$ task 1 done
Completed task 1 'test1'.
Completed 1 task.
You have more urgent tasks.
```

```bash
$ task rc.data.location:/tmp/task diag
Using alternate data.location /tmp/task

task 2.5.1
Platform: Linux

Compiler
Version: 7.3.0
Caps: +stdc +stdc_hosted +LP64 +c8 +i32 +l64 +vp64 +time_t64
Compliance: C++11

Build Features
CMake: 3.9.0
libuuid: libuuid + uuid_unparse_lower
libgnutls: 3.5.15
Build type: None

Configuration
File: /home/crem/.taskrc (found), 1941 bytes, mode 100640
Data: /tmp/task (found), dir, mode 40755
Locking: Enabled
GC: Enabled
Server:
Trust: strict
Certificate: , not readable, 0 bytes
Key: , not readable, 0 bytes
Ciphers: NORMAL
Creds:

Hooks
System: Enabled
Location: /tmp/task/hooks
(-none-)

Tests
$TERM: xterm-256color (477x143)
Dups: Scanned 2 tasks for duplicate UUIDs:
No duplicates found
Broken ref: Scanned 2 tasks for broken references:
No broken references found
```