git-gui: Reworded verify console title.

It would be something of a disservice to our users if we refer to
fsck-objects as "verify".  So instead we call it fsck-objects in
the console title, and indicate that's how we are verifying the
object database.

We probably should call our menu option "fsck-objects" or similar
but I really do think that "Verify Database" more accurately describes
the action then "fsck-objects" does, especially to users who aren't
file system developers.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>