PHP tests DOM_NOT_FOUND DOMNode::insertBefore

This commit includes 5 new phpTests to check that the error message DOM_NOT_FOUND is properly raised by the method DOMNode::insertBefore(newNode, [refNode]).  

Each file covers a different test case
- DOMNode_insertBefore_error2.phpt: covers the case when refNode is a sibling of the node where newNode wanted to be inserted.
- DOMNode_insertBefore_error3.phpt: covers  the case when refNode is the parent of the node where newNode wanted to be inserted.
- DOMNode_insertBefore_error4.phpt: covers  the case when refNode is a brand new node.
- DOMNode_insertBefore_error5.phpt: covers  the case when refNode is a descendant (not child) of the node where newNode wanted to be inserted.
- DOMNode_insertBefore_error6.phpt: covers  the case when refNode is the node where newNode wanted to be inserted.

Tested in
PHP         : /usr/bin/php 
PHP_SAPI    : cli
PHP_VERSION : 5.3.5-1ubuntu7.11
ZEND_VERSION: 2.3.0
PHP_OS      : Linux - Linux 2.6.38-16-generic #67-Ubuntu SMP Thu Sep 6 18:00:43 UTC 2012 i686
INI  : /etc/php5/cli/php.ini
More .INIs  : /etc/php5/cli/conf.d/curl.ini,/etc/php5/cli/conf.d/pdo.ini 
Extra dirs  : 
VALGRIND    : Not used