add php preview backend

lib/preview/txt.php

@@ -48,4 +48,14 @@ class TXT extends Provider{
 	}
 }
 
-\OC\Preview::registerProvider('OC\Preview\TXT');
\ No newline at end of file
+\OC\Preview::registerProvider('OC\Preview\TXT');
+
+class PHP extends TXT {
+
+	public function getMimeType() {
+		return '/application\/x-php/';
+	}
+
+}
+
+\OC\Preview::registerProvider('OC\Preview\PHP');
\ No newline at end of file