Added "legacy mode" to assembler, which is on by default.
Apparently MAC did fixups for programmers who forgot that they couldn't
put a MOVEI immediately after a JUMP or JR, so we do the same to keep
legacy code assembling (though we may flip the default to OFF at some
time in the future :-P). If you don't like the assembler doing stuff like
that behind your back, you can tell it not to by adding the -n switch to
your command line.
There are lots of other cases that the user should be warned about with
RISC code; these will be added in future commits. :-)