* Add trailing newline on non-empty list in unlines
There are several reasons to do that:
* a line in a text file is something which ends with newline,
and the last line is not special
* `unlines []` should be different from `unlines [""]`
* `unlines (a ++ b) = unlines a ++ unlines b`
* Haskell does it
* Change lines function behaviour
We've had these for a while, used for interface specialisation, but
they're not yet used anywhere else or properly documented. We should
document them soon, but for now, it's a useful performance boost to
always use the fast versions of pack/unpack/concat at runtime.
Also moves a couple to the prelude, to ensure that the fast versions are
defined in the same place as the 'normal' version so that the
transformation will always fire (that is, no need to import Data.String
for the transformation to work).
