Returns TRUE if the filename exists and is executable.
is_executable() became available with Windows in PHP version 5.0.0.
Note: The results of this function are cached. See clearstatcache() for more details.
Tip: As of PHP 5.0.0 this function can also be used with some URL wrappers. Refer to Appendix M for a listing of which wrappers support stat() family of functionality.