add external 2.1 detection and fix gd_compat for 2.1+
Merge branch 'PHP-5.3' into PHP-5.4

* PHP-5.3:
  add external 2.1 detection and fix gd_compat for 2.1+
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  add external 2.1 detection and fix gd_compat for 2.1+
Merge branch 'PHP-5.5' of git.php.net:php-src into PHP-5.5