Add libcouchbase_debug.so

This is a library where we may put extra debug
stuff the user might want to use.

Change-Id: Ib5511c1caae713b286b9373fe679826e762f9080
Reviewed-on: http://review.couchbase.org/23939
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>