max-count in terms of intersection

When a path designation is given, max-count counts the number
of commits therein (intersection), not globally.

This avoids the case where in case path has been inactive
for the last N commits, --max-count=N and path designation
at git-rev-list is given, would give no commits.

Signed-off-by: Luben Tuikov <ltuikov@yahoo.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>