Fix property and method calls on PHP native objects.

This builds on the previous pull request (the first commit unique to this pull is 44c329b) and reworks how the v8 wrapper for PHP objects works to allow properties and methods of native zend objects (that is, objects which redefine zend_handlers) as well as property set/query.  We also use higher-level methods for properties and methods wherever possible to be more compatible with magic functions.  There's a good set of test cases added for all of this as well.

The final patch refactors the template cache into the php_v8js_ctx object, and cleans it up when the context is destroyed.