Cleanup and fixes (#3273)

* newRequestID() (previously generateUploadID()) returns string than byte array.
* Remove unclear comments and added appropriate comments.
* SHA-256, MD5 Hash functions return Hex/Base64 encoded string than byte array.
* Remove duplicate MD5 hasher functions.
* Rename listObjectsValidateArgs() into validateListObjectsArgs()
* Remove repeated auth check code in all bucket request handlers.
* Remove abbreviated names in bucket-metadata
* Avoid nested if in bucketPolicyMatchStatement()
* Use ioutil.ReadFile() instead of os.Open() and ioutil.ReadAll()
* Set crossDomainXML as constant.

cmd/api-response-multipart.go

@@ -14,8 +14,6 @@
  * limitations under the License.
  */
 
-// Package cmd file carries any specific responses constructed/necessary in
-// multipart operations.
 package cmd
 
 import "net/http"
@@ -56,5 +54,3 @@ func writePartSmallErrorResponse(w http.ResponseWriter, r *http.Request, err Par
 	w.Write(encodedErrorResponse)
 	w.(http.Flusher).Flush()
 }
-
-// Add any other multipart specific responses here.