Gives precedence to user options

Previously, options set by `AutoConvert` had higher precedence than
those explicitly passed by the user. This corrects that.

imagekit/models.py

@@ -147,7 +147,8 @@ class _ImageSpecFileMixin(object):
         if getattr(self.field, 'autoconvert', True):
             autoconvert_processor = AutoConvert(format)
             img = autoconvert_processor.process(img)
-            options.update(autoconvert_processor.save_kwargs)
+            options = dict(autoconvert_processor.save_kwargs.items() + \
+                    options.items())
 
         imgfile = img_to_fobj(img, format, **options)
         content = ContentFile(imgfile.read())

imagekit/processors/__init__.py

@@ -251,6 +251,6 @@ class AutoConvert(object):
             img = bg.convert('RGB')
 
         if self.format == 'JPEG':
-            self.save_kwargs.setdefault('optimize', True)
+            self.save_kwargs['optimize'] = True
 
         return img