Add HTTP/IPP gzip support

[michaelrsweet]

Version: 1.7-feature
CUPS.org User: mike

Add support for HTTP and IPP gzip support. Should be able to respond to HTTP Accept-Encoding/Content-Encoding headers such that a client and server will be able to read and write gzip'd content transparently.

Also needs to support mid-request compression (for IPP document compression attribute support...)

[michaelrsweet]

CUPS.org User: mike

Core support is now complete and functional as of r10698. All that remains is a small change to the IPP backend to use it (and a larger change that gets rid of the "compress all files" code now that we can stream it...)

[michaelrsweet]

CUPS.org User: mike

OK, this is now implemented in trunk; the IPP backend now defaults to compressing the data sent to the printer/server if it supported gzip or deflate, and can be disabled by using the "?compression=none" option.