Launching data files from ProSel.

[johnmac@fawlty.towers.oz.au (John MacLean)]

I now have an answer to previous questions on this subject (specifically
about ProSel).

If a SYS file starts with $4C XX XX $EE $EE $40 followed by a buffer of
size $40 bytes, certain launchers are capable of launching the SYS file,
and then putting the data file name in the buffer (in P-string format).
This is how BASIC.SYSTEM launches certain applesoft programs on launch
(by default, the buffer in BASIC.SYSTEM contains "STARTUP").