Enhance collection discovering

When the request path leads to a non-existing item, try to create the
Collection object according to an existing collection at request path's
parent.

This change means that the requests whose path leads to a collection
that doesn't exist (at least MKCOL, MKCALENDAR and PUT) need to rely on
the request path more than on the Collection path. It was already done
for PUT, it's been fixed for MKCOL and MKCALENDAR.

Fix #378.

radicale/__init__.py

@@ -430,7 +430,7 @@ class Application(object):
         # TODO: use this?
         # timezone = props.get("C:calendar-timezone")
         collection = storage.Collection.create_collection(
-            collection.path, tag="VCALENDAR")
+            environ["PATH_INFO"], tag="VCALENDAR")
         for key, value in props.items():
             collection.set_meta(key, value)
         return client.CREATED, {}, None
@@ -444,7 +444,7 @@ class Application(object):
         collection = write_collections[0]
 
         props = xmlutils.props_from_request(content)
-        collection = storage.Collection.create_collection(collection.path)
+        collection = storage.Collection.create_collection(environ["PATH_INFO"])
         for key, value in props.items():
             collection.set_meta(key, value)
         return client.CREATED, {}, None