gitweb: optimize per-file history generation

gitweb: optimize per-file history generation

The rev-list command that is recent enough can filter commits
based on paths they touch, so use it instead of generating the
full list and limiting it by passing it with diff-tree --stdin.

[jc: The patch originally came from Luben Tuikov but the it was
 corrupt, but it was short enough to be applied by hand.  I
 added the --full-history to make the output compatible with the
 original while doing so.]

Signed-off-by: Junio C Hamano <junkio@cox.net>