Change "files" to "tree"

This renames the menu link and the shortcut on the repo index page from
the strange "files" to the more gittish "tree".

Suggested-by: Kristian Høgsberg <krh@bitplanet.net>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

ui-repolist.c

@@ -90,7 +90,7 @@ void cgit_print_repolist(struct cacheitem *item)
 			       "Summary", "button");
 		html("S</a>");
 		cgit_log_link("L", "Log", "button", NULL, NULL, NULL);
-		cgit_tree_link("F", "Files", "button", NULL, NULL, NULL);
+		cgit_tree_link("T", "Tree", "button", NULL, NULL, NULL);
 		html("</td></tr>\n");
 	}
 	html("</table>");