CCBC-459: Add error categories for server load and server responses
CCBC-459: Add error categories for server load and server responses

[ Ported from release23 ]

This commit adds two new error classifiers:

- LCB_ERRTYPE_SRVGEN for replies which are mapped one-to-one with a
  server reply.
- LCB_ERRTYPE_SRVLOAD for replies which unequivocally indicate the
  server is under load.

Change-Id: I51b3e8a843cf48276dbd4735526f78154f502d32
Reviewed-on: http://review.couchbase.org/39022
Tested-by: Mark Nunberg <e7d42768707bf23038325b0b68d4b577e5f6064a@haskalah.org>
Reviewed-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>

PureSwift/libcouchbase,avsej/libcouchbase,mnunberg/libcouchbase,couchbase/libcouchbase,avsej/libcouchbase,signmotion/libcouchbase,maxim-ky/libcouchbase,mnunberg/libcouchbase,PureSwift/libcouchbase,signmotion/libcouchbase,mnunberg/libcouchbase,mody/libcouchbase,senthilkumaranb/libcouchbase,kojiromike/libcouchbase,avsej/libcouchbase,mnunberg/libcouchbase,signmotion/libcouchbase,couchbase/libcouchbase,mody/libcouchbase,kojiromike/libcouchbase,senthilkumaranb/libcouchbase,couchbase/libcouchbase,PureSwift/libcouchbase,mody/libcouchbase,mnunberg/libcouchbase,kojiromike/libcouchbase,mody/libcouchbase,maxim-ky/libcouchbase,avsej/libcouchbase,couchbase/libcouchbase,avsej/libcouchbase,senthilkumaranb/libcouchbase,avsej/libcouchbase,avsej/libcouchbase,maxim-ky/libcouchbase,kojiromike/libcouchbase,maxim-ky/libcouchbase,senthilkumaranb/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,PureSwift/libcouchbase,signmotion/libcouchbase