gitk: Use the new --boundary flag to git-rev-list
gitk: Use the new --boundary flag to git-rev-list

With this, we can show the boundary (open-circle) commits immediately
after their last child, which looks much better than putting all the
boundary commits at the bottom of the graph.

Signed-off-by: Paul Mackerras <19a0ba370c443ba08d20b5061586430ab449ee8c@samba.org>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git