When discussing bug 1395079 before it was filed, config.log didn't show
"checking watchman" while it should have. We fix this here. This also
makes it printed out in the configure output (obviously), but mach
buffers that, so when configure runs through mach, it doesn't actually
show up until the result is printed out, or, if the user interrupts
configure with CTRL+C (which is better than not showing up at all in the
latter case).

--HG--
extra : rebase_source : 11a2b5c497d7b9db3ac29cb34ff0ea2a90c179c9