Xdebug isn't enabled when installed

[elazar]

1. The zend_extension line to enable Xdebug when it's installed is prepended rather than appended to php.ini.
2. The zend_extension line must include the absolute path (including the value of extension_dir) to the extension file to be enabled, where it presently only includes the filename

[jwoodcock]

@elazar Thanks for pointing this out. We'll take a look and get it fixed.