Previously, non-existent files would return -1, which is still a truthy value.
This removes the range checks for octal and binary numbers, but as a bonus Perl 6 will now report a number like 0o78 as "'78' is not a valid number", instead of previously saying "Confused". The underlying radix conversion functions properly check digits against the radix anyway (which is how the "not a valid number" error now pops up).
it used to return the value of the condition, but that doesn't help rakudo with its semantics. instead, it caused every condition of a while loop to have .sink attempted on it, even in cases where we know it doesn't make sense. so now we either have the register be an object that's null'd or set the return kind to void. Also, remove fossilized IMM_ARG mention.