Resolve the prefix to a source NickMask early instead of late.
Adding LenientDecodingLineBuffer (for consideration).
Adding hook for error handling in DecodingLineBuffer (for consideration)
Fix typo in test
Add test capturing UnicodeDecodeError
Add test to LenientDecodingLineBuffer

--HG--
extra : amend_source : 59cd70eeced2de693ea14ad6457201a1aaa03a11