Fix some bugs causing application error popups.

Specifically this should fix the following errors:

wrong # args: should be "startdiff ids" (fix from Junio Hamano)
can't read "filelines(....)": no such element in array
can't unset "treepending": no such variable
1 file changed
tree: 76d3b4ff34b3e8d33d0294a5e0b750252d51a996
  1. gitk