Make gitk save and restore window pane position on Linux and Cygwin.

Make gitk save and restore window pane position on Linux and Cygwin.

Subtle bugs remained on both Cygwin and Linux that caused the various
window panes to be restored in positions different than where the user
last placed them. Sergey Vlasov posed a pair of suggested fixes to this,
what is done here is slightly different. The basic fix here involves
a) explicitly remembering and restoring the sash positions for the upper
window, and b) using paneconfigure to redundantly set height and width of
other elements. This redundancy is needed as Cygwin Tcl has a nasty habit
of setting pane sizes to zero if their slaves are not configured with a
specific size, but Linux Tcl does not honor the specific size given.

Signed-off-by: Mark Levedahl <mdl123@verizon.net>
Signed-off-by: Junio C Hamano <junkio@cox.net>