gitk: Fix missing commits when using -S or -G

gitk: Fix missing commits when using -S or -G

When -S or -G is used as a filter option, the resulting commit list
rarely contains all matching commits. Only a certain number of commits
are displayed and the rest are missing.

"git log --boundary -S" does not return as many boundary commits as you
might expect. gitk makes up for this in closevarcs() by adding missing
parent (boundary) commits. However, it does not change $numcommits,
which limits how many commits are shown. In the end, some commits at the
end of the commit list are simply not shown.

Change $numcommits whenever a missing parent is added to the current
view.

Signed-off-by: Stefan Dotterweich <stefandotterweich@gmx.de>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>