Allow asp 4, exg 4 to shuffle tokens without coercing them into
registers; but comment why dup 4, dup 8 coerce tokens into registers.
Allow dup, dus, exg with larger sizes; and add tests dup_e.e and
exg_e.e to check that dup 20, dus, exg 20 work as well in powerpc as
in i80 and i86.
Then powerpc failed to compile loc 2 loc 4 cuu in dup_e.e. Revise the
integer conversions, so powerpc can compile and pass the test.
