Remove retval member in spl_dllist

Seems pretty useless, unless I'm missing something?
Fix invalid zend_string_frees in reflection

zend_lookup_class can share the name
Fix ::jsonSerialize() failure message
Fix incdec of referenced properties

I thought these SEPARATE_ZVAL_IF_NOT_REF usages were safe at first,
because incdec op supports reference variables. However this
violates the constraint that IS_TMP_VAR variables may not be
references (which is an issue if you use the result of the incdec
op).

Still need to fix the cases where read_property/write_property is
used.
Ensure __LINE__ is always accurate