GOCBC-193: Expose enhanced error messages.

Motivation
----------
The server now supported sending detailed error messages
as part of a failed operation.

Changes
-------
Added ability to enable enhanced error messages through a
cluster level method.  Additionally we added the ability
to fetch the underlying error cause for an error.

Change-Id: I76034dc6a3ab05a12a554ae3a44f0056cc85e491
Reviewed-on: http://review.couchbase.org/82593
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Brett Lawson <brett19@gmail.com>

cluster.go

@@ -91,6 +91,16 @@ func Connect(connSpecStr string) (*Cluster, error) {
 	return cluster, nil
 }
 
+// EnhancedErrors returns the current enhanced error message state.
+func (c *Cluster) EnhancedErrors() bool {
+	return c.agentConfig.UseEnhancedErrors
+}
+
+// SetEnhancedErrors sets the current enhanced error message state.
+func (c *Cluster) SetEnhancedErrors(enabled bool) {
+	c.agentConfig.UseEnhancedErrors = enabled
+}
+
 // ConnectTimeout returns the maximum time to wait when attempting to connect to a bucket.
 func (c *Cluster) ConnectTimeout() time.Duration {
 	return c.agentConfig.ConnectTimeout

error.go

@@ -203,3 +203,8 @@ func IsKeyExistsError(err error) bool {
 func IsKeyNotFoundError(err error) bool {
 	return gocbcore.IsErrorStatus(err, gocbcore.StatusKeyNotFound)
 }
+
+// ErrorCause returns the underlying error for an enhanced error.
+func ErrorCause(err error) error {
+	return gocbcore.ErrorCause(err)
+}