Limit memory mode at 100 buckets and return error appropriately

~~~
mc: <ERROR> Failed to create bucket for URL [http://localhost:9000/newbucket-101]. Reason: [You have attempted to create more buckets than allowed.].
~~~

Response from server

pkg/api/api_bucket_handlers.go

@@ -171,6 +171,10 @@ func (server *minioAPI) putBucketHandler(w http.ResponseWriter, req *http.Reques
 			w.Header().Set("Connection", "close")
 			w.WriteHeader(http.StatusOK)
 		}
+	case drivers.TooManyBuckets:
+		{
+			writeErrorResponse(w, req, TooManyBuckets, acceptsContentType, req.URL.Path)
+		}
 	case drivers.BucketNameInvalid:
 		{
 			writeErrorResponse(w, req, InvalidBucketName, acceptsContentType, req.URL.Path)

pkg/api/api_object_handlers.go

@@ -163,6 +163,10 @@ func (server *minioAPI) putObjectHandler(w http.ResponseWriter, req *http.Reques
 		w.WriteHeader(http.StatusOK)
 	case drivers.ObjectExists:
 		{
+			// we need to debate about this, if this is the right message to send back
+			// https://github.com/minio-io/minio/issues/505
+
+			// Ideally we can use 405 Method No Allowed
 			writeErrorResponse(w, req, NotImplemented, acceptsContentType, req.URL.Path)
 		}
 	case drivers.BadDigest:

pkg/api/api_router.go

@@ -20,12 +20,13 @@ import (
 	"log"
 	"net/http"
 
+	"time"
+
 	router "github.com/gorilla/mux"
 	"github.com/minio-io/minio/pkg/api/config"
 	"github.com/minio-io/minio/pkg/api/quota"
 	"github.com/minio-io/minio/pkg/iodine"
 	"github.com/minio-io/minio/pkg/storage/drivers"
-	"time"
 )
 
 // private use