Add LZ4 compression to WiredTiger supported

There has been some work done prototyping adding support for LZ4 compression in the WiredTiger library here: https://github.com/qconner/mongo/commits/lz4/src/third_party/wiredtiger. Thanks qconner

The characteristics of LZ4 compression are different enough to the currently supported libraries that it would be good to add support into WiredTiger.

The content in the above branch is a good start. We need to add support for building using the autoconf infrastructure in WiredTiger (as well as that for Scons in the current branch). Adding that support should be very similar to how the zlib support is currently implemented.