Merge commits from master to st2 branch

Hi,

I merged commits from master to `st2` branch. I tested and it seems to be Ok.

Actually, `u'` is only required for the character `…` in `st2`. Thus if you just keep those two lines in the `master` branch, you could delete the `st2` one :

    FILE = u'Diff file with File in Project…'
    TAB = u'Diff file with Open Tab…'

But before that, the feature `trim_trailing_white_space_before_diff` should be merged into `master`. So the plugin would be compatible with `st2` and `st3` with only one branch.

Hope it will be ok for you.