Some server needs explicit event or task when doing search

[tobixen]

• DAViCal seems not to yield results at all if doing a query that includes search filters but does not specify if we want events, tasks or journals.
• calendar.mail.ru will yield a 400 Bad Request-error when doing a query that does not specify if we want events or tasks (or journals), including the query "give me everything on the calendar" and "give me the object with the specified UID".

The test framework already supports DAViCal, and there is a hack in the object_by_uid-method to support DAViCal, but the behaviour from calendar.mail.ru is not very well supported.

Tasks:

• The object_by_uid-method already has some fallback functionality when nothing is found (supporting for DAViCal), make sure the same fallback functionality works when 400 Bad Request is returned from the calendar server
• I have for a long time had in mind that the user could give hints on what server one is connecting to when creating the client object. The idea is that the library can apply various workarounds dependent on the calendar server. In this case it would mean always passing the "event"-flag when doing searches on calendar.mail.ru, and to do separate searches for events and tasks on DAViCal and combine the results.
• The idea above should probably wait until after 1.3.10 has been released. In the meanwhile the test libary should be hacked up so that it works towards calendar.mail.ru

[tobixen]

For calendar.mail.ru, calendar.objects() will just throw a NotFoundError, even if calendar.events() yields results.

I'll work around it with a compatibility hook in the test code, but the proper solution depends on #402