Don't flag "EXPLAIN" as a write

Summary: These queries are safe to run without a CSRF token, and we need them
for the query analyzer in DarkConsole.

Test Plan: "Analyze Query Plans" works again.

Reviewers: jungejason, nh, tuomaspelkonen, aran

Reviewed By: nh

CC: aran, epriestley, nh

Differential Revision: 895

Author: epriestley

src/storage/connection/mysql/AphrontMySQLDatabaseConnection.php

@@ -209,7 +209,7 @@ public function executeRawQuery($raw_query) {
         $this->requireConnection();
 
         // TODO: Do we need to include transactional statements here?
-        $is_write = !preg_match('/^(SELECT|SHOW)\s/', $raw_query);
+        $is_write = !preg_match('/^(SELECT|SHOW|EXPLAIN)\s/', $raw_query);
         if ($is_write) {
           AphrontWriteGuard::willWrite();
         }