Ignore case for allowed extensions

Fixes error where 'image.JPG' will be disallowed when `form.upload.FileUploadField.allowed_extensions` is set to `('jpg',)`, for example.

flask_admin/form/upload.py

@@ -177,7 +177,8 @@ class FileUploadField(fields.TextField):
             return True
 
         return ('.' in filename and
-                filename.rsplit('.', 1)[1] in self.allowed_extensions)
+                filename.rsplit('.', 1)[1].lower() in
+                map(str.lower, self.allowed_extensions))
 
     def pre_validate(self, form):
         if (self.data and

flask_admin/tests/test_form_upload.py

@@ -219,6 +219,12 @@ def test_image_upload_field():
                 my_form.populate_obj(dummy)
                 eq_(dummy.upload, my_form.upload.data.filename)
 
+    # check case-sensitivity for extensions
+    filename = op.join(op.dirname(__file__), 'data', 'copyleft.jpg')
+    with open(filename, 'rb') as fp:
+        with app.test_request_context(method='POST', data={'upload': (fp, 'copyleft.JPG')}):
+            my_form = TestNoResizeForm(helpers.get_form_data())
+            ok_(my_form.validate())
 
 
 def test_relative_path():