The slow tests were supposed to run without it, except when they
explicitly requested it, but test/run always set it on the command line.
This moves it into the default config.hdf, and removes a few cases where
it was explicitly turned off in the slow tests.
I've been linking people to the README in this directory, but it is hard to see with all these files in here. What do people think about it moving a subdirectory? I don't love the name.
mwilliams