[Coco] I fixed the goddamn PCLEAR 0 bug.

[Ciaran Anscomb]

FWIW this is the bodge I have saved out for doing PCLEAR0 without such
ROM patching:

POKE183,PEEK(183)-6:POKE188,PEEK(188)-6:PCLEAR1:POKE183,PEEK(183)+6:POKE188,PEEK(188)+6

Annoyingly verbose, but should account for DOS, and works on the
Dragon too.

..ciaran