[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
Ah, I didn't realize `HAVE_ZLIB_H` will always be defined. Fair enough.