For rationale, see #6787
Extensions migrated in part 4:
* simplexml
* skeleton
* soap
* spl
* sqlite3
* sysvmsg
* sysvsem
* tidy - also removed a check for an ancient dependency version
Return the original value. If we don't return the original value,
we need to own the zval, which we don't.
For clarity also switch things to work on a zend_string* value
instead of a zval*.