Add only canonical paths to dirWatcher

Summary: KDirWatch only works correctly with canonical paths, i.e. symbolic links resolved.

Test Plan:
1. Create dirs:
$ mkdir test1
$ mkdir test1/subdir
$ ln -s test1 test2

2. Start dolphin, navigate to test2/subdir, then in terminal:
$ echo test > test2/subdir/test

Without the patch, test2/subdir/test won't be shown automatically, only after reload (F5).
With the patch applied, test2/subdir/test will be shown automatically.

3. Restart dolphin, navigate to test2/subdir, then in terminal:
$ echo test >> test2/subdir/test

Without the patch, the increased size of test2/subdir/test won't be shown automatically,
only after reload (F5). With the patch applied, it will be shown automatically.

4. Restart dolphin, navigate to test2/subdir, then in terminal:
$ rm test2/subdir/test

Without the patch, test2/subdir/test stays visible, will only disappear after reload (F5).
With the patch applied, it will disappear automatically.

Reviewers: dfaure, #dolphin, elvisangelaccio

Reviewed By: dfaure, #dolphin, elvisangelaccio

Subscribers: ngraham, elvisangelaccio, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D25732