gitweb: Harden and improve $project_filter page title

Commit 19d2d23 (gitweb: add project_filter to limit project list
to a subdirectory, 2012-01-30) added also support for displaying
$project_filter, if present, in page title.

Unfortunately it forgot to treat $project_filter as path, and escape
it using esc_path(), like it is done for $filename.

Also, it was not obvious that "$site_name - $project_filter" is about
project filtering: use "$site_name - projects in '$project_filter'".

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index f211594..877193f 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -3742,7 +3742,7 @@
 
 	unless (defined $project) {
 		if (defined $project_filter) {
-			$title .= " - " . to_utf8($project_filter);
+			$title .= " - projects in '" . esc_path($project_filter) . "'";
 		}
 		return $title;
 	}