Proper tail recursion

[Christopher T King]

Poking around in ceval.c, I discovered the PREDICT macros, and plan to
make a preliminary implementation of tail calls using a similar test (use
tail code call for any CALL_FUNCTION followed by a RETURN_VALUE). But I
was just wondering, is there any reason why LOAD_CONST and friends don't
check for a following RETURN_VALUE to avoid the push/loop/pop cycle and
rather simply return the value?