Filer: Enable delete entries without flag volume

same as happens on the s3 API on delete bucket,
to reduce the IO requests on the system, you can just clear recursively folders without flagging them in volume server (they will be removed on delete bucket/drop collection)
this will remove the user ability to retrieve data under these folders

weed/server/filer_server_handlers_write.go

@@ -280,12 +280,14 @@ func (fs *FilerServer) uploadToVolumeServer(r *http.Request, u *url.URL, auth se
 // curl -X DELETE http://localhost:8888/path/to
 // curl -X DELETE http://localhost:8888/path/to?recursive=true
 // curl -X DELETE http://localhost:8888/path/to?recursive=true&ignoreRecursiveError=true
+// curl -X DELETE http://localhost:8888/path/to?recursive=true&shouldDeleteChunks=false&shouldDeleteChunks=false
 func (fs *FilerServer) DeleteHandler(w http.ResponseWriter, r *http.Request) {
 
 	isRecursive := r.FormValue("recursive") == "true"
 	ignoreRecursiveError := r.FormValue("ignoreRecursiveError") == "true"
+	shouldDeleteChunks := !(r.FormValue("shouldDeleteChunks") == "false")
 
-	err := fs.filer.DeleteEntryMetaAndData(context.Background(), filer2.FullPath(r.URL.Path), isRecursive, ignoreRecursiveError, true)
+	err := fs.filer.DeleteEntryMetaAndData(context.Background(), filer2.FullPath(r.URL.Path), isRecursive, ignoreRecursiveError, shouldDeleteChunks)
 	if err != nil {
 		glog.V(1).Infoln("deleting", r.URL.Path, ":", err.Error())
 		writeJsonError(w, r, http.StatusInternalServerError, err)