Memory corruptions related to AST patch

Hi Nikita,

On weekend I ran PHP test suite with valgrind and opcache.
I noticed few new tests failures, that most probably introduced by AST
patch.

Bug #21820 ("$arr['foo']" generates bogus E_NOTICE, should be E_PARSE)
[tests/lang/bug21820.phpt]
Bug #66286: Incorrect object comparison with inheritance
[Zend/tests/bug66286.phpt]
unbraced complex variable replacement test (heredoc)
[Zend/tests/heredoc_005.phpt]
isset() can be used on dereferences of temporary expressions
[Zend/tests/varSyntax/issetOnTemp.phpt]

I suppose they indicate two different problems.
One of them indicates that some zvals became a subject for GC, however they
won't before. This may be fixed in opcache, but it's better to understand
what was changed.

Please take a look.

Thanks. Dmitry.