Add option to disable optimization

By default we run par test under -optimise. But occasionally we need
to test optimizations in isolation. This commit adds a Ynooptimise
flag that turns the optimize flags off back off after they've been
turned on.

A test is included to ensure that -Ynooptimise turns off optimizations
and an existing test is modified to show that optimizations coming
after -Ynooptimise in command line are enabled.