Add lcbio v2

This adds the next-generation LCB IO. This lives inside src/lcbio/* and
the tests consist of tests/ioserver (for the framework) and
tests/socktests (for the actual tests).

This commit does not adapt the core codebase to LCBIO, but rather simply
places it here.

Change-Id: Ib16e92b81874b5190f1f68393e7023547e9070af
Reviewed-on: http://review.couchbase.org/35877
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>