Implement getlastmod and getmyinode

php.net fatals on the first line of index.php on HHVM.

Let's not fatal. The first call is to getlastmod. Might as well implement getmyinode too.

Reviewed By: @ptarjan

Differential Revision: D1151025
Properly invoke setter/getter for unset declared properties

If someone manually unsets a declared property, Zend invokes __get and
__set (if present) for any future accesses to it. We were getting this right in
the interpreter but not the jit, so I fixed it by skipping the propSpecialized
case for operations that might hit this case.

Closes #684

Reviewed By: @jdelong

Differential Revision: D1158063