Configure allows misspelt options

In the latest master, ./configure --disable-optimisation (British spelling) is accepted but does nothing.

Reverting back to v0.9.0 this option makes the configure script complain right away.

I think the addition of the CSDS is the culprit here but I can't identify which specific line is creating trouble here.

This lead to an issue in a run where we thought the code was run with -O0 to help debug but wasn't due to a spelling mismatch.

We could alternatively also allow British spelling if crashing upon inappropriate --disable-xxx is problematic.