diff_tree(): Skip skip_uninteresting() when all remaining paths interesting

In 1d848f6 (tree_entry_interesting(): allow it to say "everything is interesting" 2007-03-21), both show_tree() and skip_uninteresting() were modified to determine if all remaining tree entries were interesting. However, the latter returns as soon as it finds the first interesting path, without any way to signal to its caller (namely, diff_tree()) that all remaining paths are interesting, making these extra checks useless. Pass whether all remaining entries are interesting back to diff_tree(), and whenever they are, have diff_tree() skip subsequent calls to skip_uninteresting(). With this change, I measure speedups of 3-4% for the commands $ git rev-list --quiet HEAD -- Documentation/ $ git rev-list --quiet HEAD -- t/ in git.git. Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>