Update CLib & CallASWI RMEnsures
Stub reorganisation in CLib 6.18/6.19 means that old programs which have been rebuilt and linked against new stubs may require the user to be running CLib 6.18+. So increase the CLib RMEnsure to 6.19 to make sure this new version of CLib is loaded early on in the boot sequence.
CallASWI RMEnsure has also been increased to the current version (0.20), since there have been a few important bug fixes and feature additions since the previously ensured version (0.09).
CLib RMEnsure update fixes issue reported on forums with current disc image failing to boot correctly on non-bleeding-edge ROMs: https://www.riscosopen.org/forum/forums/11/topics/17774