[PATCH 2/2] test: Have notmuch-test use the modular test collections

[Jesse Rosenthal]

These two patches, it turns out, do not quite go all the way -- they do
not set up the environment to be exactly as it was in the full test
suite. (I discovered this because my modular test suite did not fail on
the recent xapian error -- failure being success in this case.)

Further patches, which will be sent tomorrow, will take care of this in
a very naive way: essentially repeating all the steps from the original
suite up to each set of tests -- this means, of course, that the full
test suite will take longer to run, since it will have to recreate the
nm database for each collection. It's still quick enough though, and
this can be improved if we change the expected results for each tests to
conform to more uniquely tailored setups, instead of the leftovers from
previous tests.

Best,
Jesse