Disable some acc/gyros on Olimexino.
Allow the user to specify their serial port scenarios.
Configuration validation.

This enables a new feature setting for PARALLEL_PWM which is enabled by
default.

This starts to move much of the feature checking/excluding code that is
littered through into a single place - validateAndFixConfig().  Since
the config is known to be valid after the method is called other code
can just get on with it's job instead of checking for confliciting
features/settings.