git-gui: Change base version to 0.6.
git-gui: Change base version to 0.6.

This is the start of the 0.6 series of git-gui.  I'm calling it 0.6
(rather than any other value) as I already had a private tag on
one system based on 0.5, and that tag is quite a bit behind this
version.

Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>
destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git