Allow to defined legacy route mappings as a dict in config

The current code only updates the core default list if the
`ckan.legacy_route_mappings` is a string (which is probably how it comes
from the ini file). But this setting can also be set by extensions
directly on the config object, and it makes more sense to do it as a
dict.

ckan/lib/helpers.py

@@ -893,10 +893,12 @@ def build_nav(menu_item, title, **kw):
 def map_pylons_to_flask_route_name(menu_item):
     '''returns flask routes for old fashioned route names'''
     # Pylons to Flask legacy route names mappings
-    if config.get('ckan.legacy_route_mappings'):
-        if isinstance(config.get('ckan.legacy_route_mappings'), string_types):
-            LEGACY_ROUTE_NAMES.update(json.loads(config.get(
-                'ckan.legacy_route_mappings')))
+    mappings = config.get('ckan.legacy_route_mappings')
+    if mappings:
+        if isinstance(mappings, string_types):
+            LEGACY_ROUTE_NAMES.update(json.loads(mappings))
+        elif isinstance(mappings, dict):
+            LEGACY_ROUTE_NAMES.update(mappings)
 
     if menu_item in LEGACY_ROUTE_NAMES:
         log.info('Route name "{}" is deprecated and will be removed.\

ckan/tests/controllers/test_home.py

@@ -63,6 +63,19 @@ def test_map_pylons_to_flask_route(self):
         response = app.get(url_for('my_home_route'))
         assert 'Welcome to CKAN' in response.body
 
+        response = app.get(url_for('home'))
+        assert 'Welcome to CKAN' in response.body
+
+    @helpers.change_config('ckan.legacy_route_mappings',
+                           {'my_home_route': 'home.index'})
+    def test_map_pylons_to_flask_route_using_dict(self):
+        app = self._get_test_app()
+        response = app.get(url_for('my_home_route'))
+        assert 'Welcome to CKAN' in response.body
+
+        response = app.get(url_for('home'))
+        assert 'Welcome to CKAN' in response.body
+
 
 class TestI18nURLs(helpers.FunctionalTestBase):