Fixed bug (is_callable() triggers Fatal Error)

This bug is also exists in 5.4, and previous fix by dsp is not complete
for __callStatic stituation, see test script
Merge branch 'PHP-5.4' into PHP-5.5

Conflicts:
	Zend/zend_API.c
Merge branch 'PHP-5.5' of git.php.net:php-src into PHP-5.5
Merge branch 'PHP-5.5'