gitweb: Make JavaScript ability to adjust timezones configurable

Configure JavaScript-based ability to select common timezone for git
dates via %feature mechanism, namely 'javascript-timezone' feature.

The following settings are configurable:
* default timezone (defaults to 'local' i.e. browser timezone);
  this also can function as a way to disable this ability,
  by setting it to false-ish value (undef or '')
* name of cookie to store user's choice of timezone
* class name to mark dates

NOTE: This is a bit of abuse of %feature system, which can store only
sequence of values, rather than dictionary (hash); usually but not
always only a single value is used.

Based-on-code-by: John 'Warthog9' Hawley <warthog9@eaglescrag.net>
Helped-by: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -480,6 +480,18 @@ sub evaluate_uri {
 		'override' => 0,
 		'default' => [0]},
 
+	# Enable and configure ability to change common timezone for dates
+	# in gitweb output via JavaScript.  Enabled by default.
+	# Project specific override is not supported.
+	'javascript-timezone' => {
+		'override' => 0,
+		'default' => [
+			'local',     # default timezone: 'utc', 'local', or '(-|+)HHMM' format,
+			             # or undef to turn off this feature
+			'gitweb_tz', # name of cookie where to store selected timezone
+			'datetime',  # CSS class used to mark up dates for manipulation
+		]},
+
 	# Syntax highlighting support. This is based on Daniel Svensson's
 	# and Sham Chukoury's work in gitweb-xmms2.git.
 	# It requires the 'highlight' program present in $PATH,
@@ -3733,14 +3745,19 @@ sub git_footer_html {
 		      qq!           "!. href() .qq!");\n!.
 		      qq!</script>\n!;
 	} else {
+		my ($jstimezone, $tz_cookie, $datetime_class) =
+			gitweb_get_feature('javascript-timezone');
+
 		print qq!<script type="text/javascript">\n!.
-		      qq!window.onload = function () {\n!.
-		      (gitweb_check_feature('javascript-actions') ?
-		      qq!	fixLinks();\n! : '').
-		      # last parameter to onloadTZSetup must be CSS class used by format_timestamp_html
-		      qq!	var tz_cookie = { name: 'gitweb_tz', expires: 14, path: '/' };\n!. # in days
-		      qq!	onloadTZSetup('local', tz_cookie, 'datetime');\n!.
-		      qq!};\n!.
+		      qq!window.onload = function () {\n!;
+		if (gitweb_check_feature('javascript-actions')) {
+			print qq!	fixLinks();\n!;
+		}
+		if ($jstimezone && $tz_cookie && $datetime_class) {
+			print qq!	var tz_cookie = { name: '$tz_cookie', expires: 14, path: '/' };\n!. # in days
+			      qq!	onloadTZSetup('$jstimezone', tz_cookie, '$datetime_class');\n!;
+		}
+		print qq!};\n!.
 		      qq!</script>\n!;
 	}
 
@@ -3946,7 +3963,13 @@ sub git_print_section {
 
 sub format_timestamp_html {
 	my $date = shift;
-	my $strtime = '<span class="datetime">'.$date->{'rfc2822'}.'</span>';
+	my $strtime = $date->{'rfc2822'};
+
+	my (undef, undef, $datetime_class) =
+		gitweb_get_feature('javascript-timezone');
+	if ($datetime_class) {
+		$strtime = qq!<span class="$datetime_class">$strtime</span>!;
+	}
 
 	my $localtime_format = '(%02d:%02d %s)';
 	if ($date->{'hour_local'} < 6) {