Fix #12545: Refactor print_timezone_option_list()

This function was not producing well formed XHTML due to missing closing
tags on the <optgroup> elements. It was also neglecting to send line
breaks and tabs to the output engine for each option printed, causing
very long lines to appear in the XHTML output. Shorter lines are easier
to read through and debug.

account_prefs_inc.php

@@ -293,7 +293,7 @@ function edit_account_prefs($p_user_id = null, $p_error_if_protected = true, $p_
 	</th>
 	<td>
 		<select name="timezone">
-			<?php print_timezone_option_list( $t_pref->timezone ?  $t_pref->timezone  : config_get_global( 'default_timezone' ) ) ?>
+<?php print_timezone_option_list( $t_pref->timezone ?  $t_pref->timezone  : config_get_global( 'default_timezone' ) ) ?>
 		</select>
 	</td>
 </tr>

core/print_api.php

@@ -1667,7 +1667,7 @@ function swap_content( span ) {
 # Print the option list for timezones
 function print_timezone_option_list( $p_timezone ) {
 	if ( !function_exists( 'timezone_identifiers_list' ) ) {
-		echo '<option value="', $p_timezone, '" selected="selected">', $p_timezone, '</option>';
+		echo "\t<option value=\"$p_timezone\" selected=\"selected\">$p_timezone</option>\n";
 		return;
 	}
 
@@ -1697,11 +1697,12 @@ function print_timezone_option_list( $p_timezone ) {
 	}
 
 	foreach( $t_locations as $t_continent => $t_locations ) {
-		echo '<optgroup label="'.$t_continent.'">';
+		echo "\t<optgroup label=\"$t_continent\">\n";
 		foreach ( $t_locations as $t_location ) {
-			echo '<option value="' . $t_location[1] . '"';
+			echo "\t\t<option value=\"" . $t_location[1] . '"';
 			check_selected( $p_timezone, $t_location[1] );
-			echo '>' . $t_location[0] . '</option>';
+			echo '>' . $t_location[0] . "</option>\n";
 		}
+		echo "\t</optgroup>\n";
 	}
 }