Fix name of EX AF,AF' instruction
The issue here is that EXX only exchanges the BC, DE and HL registers with the shadow registers BC', DE' and HL'. It does not exchange AF and AF', and to do that, a separate instruction,
EXX AF,AF' is required.
This bug was later fixed by MGT for the +D, in G+DOS. The bug is similarly absent from the [[Messenger]], a product by SAMCo (formed on the assets of MGT after it went into receivership) for transferring Spectrum snapshots to/from a SAM Coupé — both in the shadow ROM for the Spectrum, and in the companion software that runs on the Coupé.