implement clock_gettime(CLOCK_MONOTONIC)

It's bad to pretend to support every clock - we should correctly return -1 with EINVAL for the clocks we don't implement. It's also nice to give implementations a way to detect if they have access to a monotonic clock. For comparison, old Linux machines (RHEL 3 for example) don't have CLOCK_MONOTONIC, new ones do.
fix formatting and a bug in clock_getres, and add unittest
Merge branch 'monotonicclock' of https://github.com/NWilson/emscripten into incoming

Conflicts:
	emscripten-version.txt
print out failing js engine in test runner
fix test_posixtime for v8, which lacks monotonic time, and add testing for that path