Automatically define _INPLACE variables for perl programs too

and use them for split
Use the automatic variables for touchy too
Automatically add the $(exeext) to program names

We now define _PROGNAME, and _PROG is automatically defined with
$(exeext). This will shortly automatically use the right exeext
depending on what stage it is being compiled with (exeext may be
different for different stages when cross-compiling).
Merge branch 'master' of darcs.haskell.org:/srv/darcs//ghc