Fixup the content of error messages in rlm_pap

Have rlm_pap return more specific errors depending on what went wrong, if digest lengths weren't what we were expecting the request (as a whole) is INVALID so we should return INVALID and NOT REJECT.

Fixup code formatting
if (<cond>)
	<body>

Is not allowed
Rename 'binbuf' to 'digest' in rlm_pap (consistent with the xlat functions)
Correct sha1 tests
Add support for SHA-2 digests