Make zend_parse_parameters share fast zpp implementation where possible

Since I don't like duplication, here's a patch that makes zend_parse_parameters use the fast zpp internal functions to do parameter parsing where possible, which so zpp and fast zpp share implementations. I think that'd be good as it'd mean that for most parameter types there's only one implementation of the parsing code.

This currently can't be safely merged, since if PHP's compiled with FAST_ZPP set to 0, then the fast zpp functions don't exist. Would it be reasonable to make the internal fast zpp functions always be available, and make FAST_ZPP only control the presence of the macros? :)