fs: Cleanup Golang errors to be called 'e' and probe to be called as 'err'

- Replace the ACL checks back, remove them when bucket
  policy is implemented.
- Move FTW (File Tree Walk) into ioutils package.

signature-handler.go

@@ -44,6 +44,13 @@ func isRequestSignatureV4(req *http.Request) bool {
 	return false
 }
 
+func isRequestRequiresACLCheck(req *http.Request) bool {
+	if isRequestSignatureV4(req) || isRequestPresignedSignatureV4(req) || isRequestPostPolicySignatureV4(req) {
+		return false
+	}
+	return true
+}
+
 func isRequestPresignedSignatureV4(req *http.Request) bool {
 	if _, ok := req.URL.Query()["X-Amz-Credential"]; ok {
 		return ok