`sets.Set` has been deprecated in favor of `set` since 2.6, and
`string.maketrans` has to be special cased. In Python 3 there
is `str.maketrans`, `bytes.maketrans`, and `bytearray.maketrans`
and you have to choose the correct one. So we need to introduce
a runtime version check at this site.
llvm-svn: 252348