parse2.py: restore accidently-removed while1stmt rule
scanner27.py: grammar typo
check_ast: add while1else to list of looping constructs
pysource.py: CALL_FUNCTION_VAR_KW_ARGS with positional args rule is different?
Until we can actually prevent these in grammar rules, we will warn of
improper decompilations.
Also, we now stop when we hit a decompile error. Previously we were not.