gitweb: Enable tree (directory) history display

This patch allows history display of whole trees/directories a la
"git-rev-list HEAD -- <dir or file>".  I find this useful especially
when a project lives in its own subdirectory, as opposed to being all
of the GIT repository (i.e. when a sub-project is merged into a
super-project).
Signed-off-by: NLuben Tuikov <ltuikov@yahoo.com>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

gitweb/gitweb.cgi

@@ -1676,6 +1676,7 @@ sub git_tree {
 			      "</td>\n" .
 			      "<td class=\"link\">" .
 			      $cgi->a({-href => "$my_uri?" . esc_param("p=$project;a=tree;h=$t_hash$base_key;f=$base$t_name")}, "tree") .
+			      " | " . $cgi->a({-href => "$my_uri?" . esc_param("p=$project;a=history;h=$hash_base;f=$base$t_name")}, "history") .
 			      "</td>\n";
 		}
 		print "</tr>\n";