fix(File): add support to following use cases

us: data = { blob: Buffer }
e1: data = Buffer

Author: leeyeh

src/file.js

@@ -385,15 +385,14 @@ module.exports = function(AV) {
         data.blob.type = guessedType;
       }
       this._source = AV.Promise.as(data.blob, guessedType);
-    } else if (typeof(File) !== "undefined" && data instanceof global.File) {
+    } else if (typeof File !== "undefined" && data instanceof global.File) {
       this._source = AV.Promise.as(data, guessedType);
-    } else if (avConfig.isNode && global.Buffer.isBuffer(data)) {
+    } else if (typeof Buffer !== "undefined" && global.Buffer.isBuffer(data)) {
       // use global.Buffer to prevent browserify pack Buffer module
-      this.attributes.base64 = data.toString('base64');
-      this._source = AV.Promise.as(this.attributes.base64, guessedType);
       this.attributes.metaData.size = data.length;
+      this._source = AV.Promise.as(data, guessedType);
     } else if (_.isString(data)) {
-      throw "Creating a AV.File from a String is not yet supported.";
+      throw new Error("Creating a AV.File from a String is not yet supported.");
     }
   };
 
@@ -720,6 +719,9 @@ module.exports = function(AV) {
             if (this.attributes.base64) {
               data.base64 = this.attributes.base64;
               return AV._request('files', this.attributes.name, null, 'POST', data);
+            } else if (typeof Buffer !== "undefined" && global.Buffer.isBuffer(file)) {
+              data.base64 = file.toString('base64');
+              return AV._request('files', this.attributes.name, null, 'POST', data);
             } else {
               return readAsync(file).then(function(base64) {
                 data.base64 = base64;

test/file.js

@@ -53,22 +53,15 @@ describe('files', function() {
     });
   });
 
-  if(AV._isNode){
+  if(typeof Buffer !== 'undefined'){
     describe('Saving buffer in node.js', function() {
-      it('should be saved', function(done) {
+      it('should be saved', function() {
           var file = new AV.File('myfile.txt', new Buffer('hello world'));
-          file.save().then(function() {
+          return file.save().then(function() {
             expect(file.size()).to.be(11);
             expect(file.ownerId()).to.be.ok();
             expect(file.id).to.be.ok();
-            expect(file.thumbnailURL(200, 100)).to.be(file.url() + '?imageView/2/w/200/h/100/q/100/format/png');
-            file.destroy().then(function() {
-              done();
-            }, function(error) {
-              done(error);
-            });
-          }, function(error) {
-            done(error);
+            return file.destroy();
           });
       });
     });