GOCBC-119: Update N1qlQuery.Custom to support interface{}.
GOCBC-119: Update N1qlQuery.Custom to support interface{}.

This fixes an issue where passing non-string types as a custom
parameter to a N1QL query was not possible.

Change-Id: Id68346e143af6dbe51b63813da67b6b938e07584
Reviewed-on: http://review.couchbase.org/70825
Reviewed-by: Mark Nunberg <dab05a0fe859c5cb93882b2a75a0d613501b07be@couchbase.com>
Tested-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>

brett19/gocb