gitweb: do not run "git diff" that is Porcelain

Jakub says that legacy-style URI to view two blob differences are never
generated since 1.4.3.  This codepath runs "git diff" Porcelain from the
gitweb, which is a no-no.  It can trigger diff.external command that is
specified in the configuration file of the repository being viewed.

This patch applies to v1.5.4 and later.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -4809,43 +4809,9 @@ sub git_blobdiff {
 			or die_error(undef, "Open git-diff-tree failed");
 	}
 
-	# old/legacy style URI
-	if (!%diffinfo && # if new style URI failed
-	    defined $hash && defined $hash_parent) {
-		# fake git-diff-tree raw output
-		$diffinfo{'from_mode'} = $diffinfo{'to_mode'} = "blob";
-		$diffinfo{'from_id'} = $hash_parent;
-		$diffinfo{'to_id'}   = $hash;
-		if (defined $file_name) {
-			if (defined $file_parent) {
-				$diffinfo{'status'} = '2';
-				$diffinfo{'from_file'} = $file_parent;
-				$diffinfo{'to_file'}   = $file_name;
-			} else { # assume not renamed
-				$diffinfo{'status'} = '1';
-				$diffinfo{'from_file'} = $file_name;
-				$diffinfo{'to_file'}   = $file_name;
-			}
-		} else { # no filename given
-			$diffinfo{'status'} = '2';
-			$diffinfo{'from_file'} = $hash_parent;
-			$diffinfo{'to_file'}   = $hash;
-		}
-
-		# non-textual hash id's can be cached
-		if ($hash =~ m/^[0-9a-fA-F]{40}$/ &&
-		    $hash_parent =~ m/^[0-9a-fA-F]{40}$/) {
-			$expires = '+1d';
-		}
-
-		# open patch output
-		open $fd, "-|", git_cmd(), "diff", @diff_opts,
-			'-p', ($format eq 'html' ? "--full-index" : ()),
-			$hash_parent, $hash, "--"
-			or die_error(undef, "Open git-diff failed");
-	} else  {
+	# old/legacy style URI -- not generated anymore since 1.4.3.
+	if (!%diffinfo) {
 		die_error('404 Not Found', "Missing one of the blob diff parameters")
-			unless %diffinfo;
 	}
 
 	# header