Fix XSS in search page

Dmitry Ivanov [d1m0ck](https://twitter.com/d1m0ck) reported[*1] a
security vulnerability in the Source Integration plugin's search results
page, allowing an attacker to inject arbitrary HTML or javascript code
(the latter, only if MantisBT's default CSP are disabled).

Proper escaping of the permalink resolves the issue.

Fixes #205

[*1]: http://openbugbounty.org/incidents/218993/

Source/pages/search.php

@@ -37,10 +37,10 @@
 				<div class="table-responsive">
 
 					<div class="widget-toolbox padding-8 clearfix">
-						<a class="btn btn-xs btn-primary btn-white btn-round" href="<?php echo plugin_page( 'search' ) . $t_permalink ?>">
+						<a class="btn btn-xs btn-primary btn-white btn-round" href="<?php echo plugin_page( 'search' ) . string_attribute( $t_permalink ) ?>">
 							<?php echo plugin_lang_get( 'permalink' ) ?>
 						</a>
-						<a class="btn btn-xs btn-primary btn-white btn-round" href="<?php echo plugin_page( 'search_page' ) . $t_permalink ?>">
+						<a class="btn btn-xs btn-primary btn-white btn-round" href="<?php echo plugin_page( 'search_page' ) . string_attribute( $t_permalink ) ?>">
 							<?php echo plugin_lang_get( 'modify_search' ) ?>
 						</a>
 						<a class="btn btn-xs btn-primary btn-white btn-round" href="<?php echo plugin_page( 'search_page' ) ?>">