git-instaweb: Change how gitweb.psgi is made runnable as standalone app

According to blog post "FindBin, __FILE__, $0 and PSGI woes"

  http://bulknews.typepad.com/blog/2011/02/findbin-__file__-0-and-psgi-woes.html

by Tatsuhiko Miyagawa, using 'if (__FILE__ eq $0)' in .psgi code
(to check if script was run from command line), is not supposed to work
since Plack 0.9971.

Replace it with one of proposed solutions; while at it return $app
explicitely, rather than implicitely by being a last expression.

This affects 'plackup' web server.

While at it cleanup whitespace.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Acked-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-instaweb.sh

@@ -558,12 +558,14 @@ my \$app = builder {
 
 # make it runnable as standalone app,
 # like it would be run via 'plackup' utility
-if (__FILE__ eq \$0) {
+if (caller) {
+	return \$app;
+} else {
 	require Plack::Runner;
 
 	my \$runner = Plack::Runner->new();
 	\$runner->parse_options(qw(--env deployment --port $port),
-			       "$local" ? qw(--host 127.0.0.1) : ());
+				"$local" ? qw(--host 127.0.0.1) : ());
 	\$runner->run(\$app);
 }
 __END__