Make email "source" filter use a dropdown, in bouncer UI.

tailbone/grids/search.py

@@ -85,6 +85,23 @@ class BooleanSearchFilter(SearchFilter):
                            ["True", "False"])
 
 
+class ChoiceSearchFilter(SearchFilter):
+    """
+    Generic search filter where the user may only select among a specific set
+    of choices.
+    """
+
+    def __init__(self, choices):
+        self.choices = choices
+
+    def __call__(self, name, label=None, **kwargs):
+        super(ChoiceSearchFilter, self).__init__(name, label=label, **kwargs)
+        return self
+
+    def value_control(self):
+        return tags.select(self.name, self.search.config.get(self.name), self.choices)
+
+
 def EnumSearchFilter(enum):
     options = enum.items()