Have gzputc return the character written instead of the argument.
Have gzputc return the character written instead of the argument.

When successful, gzputc would return the second argument.  If the
second argument were -1, gzputc would return -1 instead of the
character written, which was 255.  However the -1 would not be
distinguishable from an error.  Now gzputc returns 255 in that
case.

Streamlet/ZLibWrap,Streamlet/ZLibWrap,Streamlet/ZLibWrap,Streamlet/ZLibWrap,Streamlet/ZLibWrap