Experiment with lz4 compression

[joerivanruth]

To speed up the transfer phase.

Add a small hack to the server to optionally lz4 decompress uploaded data.
(Compressing the whole mapi exchange is a larger project)

Suggested syntax:
COPY BINARY INTO mytable FROM files ON 'lz4' CLIENT

Because it's only applicable to ON CLIENT.

[joerivanruth]

Implemented. Will be part of the next feature release.