Decode FHCRC flag properly, as per Internet RFC 1952.

Decode FHCRC flag properly, as per Internet RFC 1952.

Problem reported by Greg Roelofs in:
http://lists.gnu.org/archive/html/bug-gzip/2010-06/msg00003.html

* gzip.c (discard_input_bytes): New function.
(get_method): Check header checksum, if given.  We never generate it,
but other programs may.
* gzip.h (HEADER_CRC): Renamed from CONTINUATION.  All uses changed.
* tailor.h [defined __50SERIES]: Remove PRIMOS stuff that was obsolete
anyway and would have made this patch harder to maintain.
(get_char, put_char): Remove.
* zip.c (zip): Use put_byte instead of the now-removed put_char.