Before this change, both test-book-meta-backend and test-cal-meta-backend
failed when there was no evolution-source-registry running. This change
fixes it and makes sure correct source registry is used, like the one
from the build directory, not the system one.

There is no '.libs' in the build directory since the move to CMake,
but some tests still referenced it.

One change related specifically for Google servers, to not try twice when
the first load fails with "404 Not Found".

The other change is to verify that the collection on the server did change
meanwhile. If it did, then it's possible it was due to the component which
is not in the local cache yes, thus try to load it. If the collection did
not change, then it means the local cache is up-to-date with the server
content, thus the to-be-loaded object is not on the server, thus no need
to poke it and receive failure anyway. This works only if the server
supports getctag extension.