DECOMPRESS/GZIP fix

changes details:
-fixed refinement/arg bug in DECOMPRESS
-fixed CRC32 calculation/verification in ZLIB code in DECOMPRESS/GZIP mode

Carl, maybe it would be better to change the /GZIP refinement to /CRC32 ? What do you think?
I think it is better as the feature is not fully compatible with GZIP format but it just uses different checksum type (instead of the default adler-32)
We can always write the higher-level formats (ZIP, GZIP etc.) in REBOL instead of hardcoding into the native code.