Statusbar and parallel diff

[Kai Willadsen <kai willadsen gmail com>]

Hi all,

I've just pushed a couple of significant feature branches to current Git.

The first is the addition of a new status bar class which handles
things better. With this new statusbar, menu and toolbar action
tooltips should actually appear in the current place and won't be
ellipsized, and our task status is now packed into the progress bar
for compactness. Each individual view (file, folder, VC) now has its
own status bar extra-information areas to use as they will; this may
be useful in merge mode.

The second feature is that inline highlighting is now done in parallel
(using Python's multiprocessing). We also keep track of which diff
chunks have changed so that we know what needs to be re-highlighted.
The upshot is that all comparison highlighting should be faster, and
in particular, interactive performance while editing should be vastly
improved.

Testing and feedback welcome, as always.

cheers,
Kai