build_runtime_definition_key returns zend_string*
Formatting
Fix segfault when class name evaluates to IS_CONST
Immutablize constant leaf arrays

Still haven't entirely figured out how to elegantly handle the
recursive variant.
Immutable arrays for the recursive case as well
Weaker recursion during pre-evaluation
Rename _tmp_compile_const_expr

Also remove recursive immutization of arrays there, because this
is already handled when the array is created.
Use ZVAL_COPY until proven wrong
Mark some small functions as inline
Support doc comments for propreties