git-gui: Display tooltips in blame viewer
git-gui: Display tooltips in blame viewer

When the mouse is over a particular line and we have blame data
for that line, but its not the active commit, we should show the
user information about that commit like who the author was and
what the subject (first line) was.

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