Fill port with a corrupted data in debug (TRASH it) in order to
detect double port destruction early.

Add a comment for func_call function that describes what states
of ports are expected before and after func_call.

Fix port usage in lua using ffi - allocate a full port structure
instead of a (bit smaller) structure port_c. That makes any port
structure to have fixed determined size which in turn makes safe
to cast and use different port types.

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=refactoring