Run profiling tests automatically

[rrthomas]

Having managed to regress rather dramatically on performance, we should be running the tests all the time so we can detect this sooner.

[rrthomas]

Needed:

• In configure.ac check for perf and valgrind
• When running the tests with perf, check the kernel has been correctly set up, and warn the user if not.
• Extract just peak memory usage from massif.