Work in progress, but largely works. Known issues:
* only supported when using the timeout program
* 'test.strace' files aren't cleaned, as they end up in the root
  directory rather than the test's directory
* Doesn't yet track what the current directory is, so finds several
  files like "A.o" being written by multiple tests (and conversely,
  may be missing writes to the same file from different directories)
* Lots of tests write to $HOME/.ghc/ghci_history. We should probably
  be passing ghci a flag to stop this from happening.
* Some .strace lines aren't understood yet, causing framework failures
* One .strace file can cause muiltiple framework failures, if it
  contains lots of lines that aren't understood

Performance:
Threads       fast testsuite time     fast testsuite time with checks
1             16:36.14                25:16.07
5              5:33.95                 8:04.05