[Reviewer: Andy] Add compressed parameter support

Andy,

Please can you review (but not merge) my changes to SAS client to support compressed parameters.  Once you've reviewed, I'll ask the SAS team to review too.

I haven't live-tested this yet - waiting for your bits.  I also need to look at sas-client UT.

Matt
`gcc` is smart enough and the Makefile is hard-coded to use this, so I'm not too bothered about other compilers.

With regard to `#if` vs `#ifdef`, `HAVE_ZLIB_H` takes a 0 or a 1, so `#if` is correct (and this is consistent with the other `HAVE_*_H` constants defined in `include/config.h`.