depends filter does not work with IDs

#### To report a bug...

* What command(s) did you run?
```
% task rc.data.location:/tmp/task add test
Using alternate data.location /tmp/task
Created task 1.
Configuration override rc.data.location:/tmp/task
% task rc.data.location:/tmp/task add test2 depends:1
Using alternate data.location /tmp/task
Created task 2.
Configuration override rc.data.location:/tmp/task
% task rc.data.location:/tmp/task next depends:1
Using alternate data.location /tmp/task
Configuration override rc.data.location:/tmp/task
No matches.
```
* What did you expect to happen?
I expected that the final output results in listing the task with ID 2.
* What actually happened?
The output was empty.

This was discussed extensively earlier today over in the #taskwarrior irc channel. We found out that the `depends` filter does work but only with UUIDs. In the "rare" case where the ID matches the beginning of the UUID the above scenario might indeed appear to be working, however, in general it does not.
This contradict the man page where it is stated that:
```
depends:
Declares this task to be dependent on id1 and id2. This means that the tasks id1 and id2 should be completed before this task. Consequently, this task will then show up on the 'blocked' report. It accepts a comma-separated list of
ID numbers, UUID numbers and ID ranges. When prefixing any element of this list by '-', the specified tasks are removed from the dependency list.
```
(at least assuming that the same syntax can be used for a filter...)

* Paste the output of the ```task diag``` command.
```
% task diag
task 2.5.1
Platform: Linux

Compiler
Version: 8.2.1 20180831
Caps: +stdc +stdc_hosted +LP64 +c8 +i32 +l64 +vp64 +time_t64
Compliance: C++11

Build Features
Built: Nov 9 2018 23:33:36
CMake: 3.12.4
libuuid: libuuid + uuid_unparse_lower
libgnutls: 3.5.19
Build type:

Configuration
File: overwritten in example above
Data: overwritten in example above
Locking: Enabled
GC: Enabled
$EDITOR: nvim
Server:
CA:
Trust: strict
Certificate:
Key:
Ciphers: NORMAL
Creds:

Hooks
System: Enabled
Location: /home/max/.task/hooks
Active: on-modify.timewarrior (executable) (symlink)
Inactive:

Tests
$TERM: tmux-256color (376x102)
Dups: Scanned 763 tasks for duplicate UUIDs:
No duplicates found
Broken ref: Scanned 763 tasks for broken references:
No broken references found

```