[nextgen-gallery] Fix identifiers quoted as strings

MySQL allows quoting identifiers, such as column names, as strings using
single-quotes in addition to quoting as identifiers using grave accents.
PostgreSQL does not, resulting in errors such as:

Error running :
SELECT DISTINCT wp_ngg_pictures.* , GROUP_CONCAT(CONCAT_WS('@@', meta_key, meta_value)) AS 'extras' FROM `wp_ngg_pictures` LEFT OUTER JOIN `wp_postmeta` ON `wp_postmeta`.`post_id` = `extras_post_id`  GROUP BY wp_ngg_pictures.pid LIMIT 1
---- converted to ----
SELECT DISTINCT wp_ngg_pictures.* , GROUP_CONCAT(CONCAT_WS('@@', meta_key, meta_value)) AS 'extras' FROM wp_ngg_pictures LEFT OUTER JOIN wp_postmeta ON wp_postmeta.post_id = extras_post_id  GROUP BY wp_ngg_pictures.pid LIMIT 1
----> ERROR:  syntax error at or near "'extras'"
LINE 1: ..._CONCAT(CONCAT_WS('@@', meta_key, meta_value)) AS 'extras' F...
                                                             ^

Fix this by replacing single quotes with grave accents when they occur
after ") AS ".  This strategy obviously has both false-positive and
false-negative issues, but suits the current needs and should be
relatively safe from false-positives.  Proper replacement would require
parsing the SQL.

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>

pg4wp/driver_pgsql.php

@@ -292,6 +292,11 @@
 			if( false !== strpos( $sql, $wpdb->comments))
 				$sql = str_replace(' comment_id ', ' comment_ID ', $sql);
 			
+			// MySQL supports strings as names, PostgreSQL needs identifiers.
+			// Limit to after closing parenthesis to reduce false-positives
+			// Currently only an issue for nextgen-gallery plugin
+			$pattern = '/\) AS \'([^\'])\'/';
+			$sql = preg_replace( $pattern, ') AS "$1"', $sql);
 		} // SELECT
 		elseif( 0 === strpos($sql, 'UPDATE'))
 		{