#68 Fixes required for Tree Browser plugin

[Nathan B]

I would like to please request the following fixes for the TreeBrowser plugin:

1. When right-clicking on a file or directory, that file or directory should become selected before the context menu is shown.
At the moment, the user must first left-click, before right-clicking. [1]

2. When renaming a file, you should not show the 'do you really want to replace it?' warning message if the filename has not changed.

3. If I create an empty directory, then highlight '(Empty)' and right click it, the 'Create new directory' and 'Create new file' commands do nothing.

4. The 'delete' key should delete a file.

[1] This is a duplicate of this bug: https://sourceforge.net/tracker/?func=detail&aid=3440602&group_id=222729&atid=1056532

[Nathan B]

I have fixed 1, 2, and 3. Will send a pull request for these patches as soon as geany-plugins is transferred to github.