Plone.app.caching

- Fix tests that fail on the day before the switch to daylight saving time.
[pbauer]

- Use the PLONE_APP_CONTENTTYPES_FIXTURE test layer for Plone 5 compatibility.
[timo]

- Make it possible to set a maxage of zero in strong caching. This is
an edge case since this would ordinarily be handled by moderate caching.
[smcmahon]

- Add some testing for weak caching operations.
[smcmahon]

- Fix handling of anon-only flag for cases where maxage is not zero. It
was effectively ignored. Added operation test for strong caching.
[smcmahon]

- Fix double purge of paths for items whose default view is the same as /view
[eleddy]

- Register the plone.atobjectfields adapter not only when Products.Archetypes
but also plone.app.blob is installed.
[thet]

- Fixed purge paths for virtual hosting scenarios using virtual path components.
[dokai]