Nicer error message for #3782
It now says: ghc-stage2: sorry! (this is work in progress) (GHC version 7.1.20101028 for i386-apple-darwin): Vectorise.Builtins.indexBuiltin DPH builtin function 'sumTyCon' of size '11' is not yet implemented. This function does not appear in your source program, but it is needed to compile your code in the backend. This is a known, current limitation of DPH. If you want it to to work you should send mail to email@example.com and ask what you can do to help (it might involve some GHC hacking). I added 'pprSorry' that behaves like 'pprPanic' except it say sorry! instead of panic!, and doesn't ask the user to report a bug.