For rationale, see https://github.com/php/php-src/pull/6787
Make extension checks lowercase, add a special case for opcache
that has internal name not matching .so filename.
Extensions migrated in part 2:
* dom
* exif
* fileinfo
* ffi
Each file covers a different test case
DOMNode_insertBefore_error2.phpt: refNode is a sibling of the node where newNode wanted to be inserted.
DOMNode_insertBefore_error3.phpt: refNode is the parent of the node where newNode wanted to be inserted.
DOMNode_insertBefore_error4.phpt: refNode is a brand new node.
DOMNode_insertBefore_error5.phpt: refNode is a descendant (not child) of the node where newNode wanted to be inserted.
DOMNode_insertBefore_error6.phpt: refNode is the node where newNode wanted to be inserted.