JSCBC-154: Corrected Error class not being attached in JS-Land.

Change-Id: I77377a9320a10a491f5b86a2b74f71589298f04c
JSCBC-155: Remove reference to expiry in append/prepend.

Append/Prepend commands do not support specifying an expiry
time at the binary protocol level, and we were exposing
these parameters in error.

Change-Id: I7dfe6d8e96e500f0778dd5af86b9fb6fb9e195e9
Update to latest libcouchbase (2.4.3)

Change-Id: I635252221ebb18f369a8f4f29769bf090594c31b
JSCBC-157: Flush lcb network buffers at end of Node.js frame.

This provides better network performance when performing multiple
operations within the same tick.  Only 1 network flush occurs prior
to node blocking for IO rather than one per operation.

Change-Id: Ib7ffe13d11dbc6ce66df284f5d0825097739f677