On OS X, fix the path to the libffi dynlib; fixes #7833
Run "sh ./configure" rather than "sh configure"; part of #7992

This fixes a bug with how configure re-execs itself.
Fix the dynmaic library paths in the libs, as well as in the programs

Part of #7833
Fix dynlib paths in the RTS too; part of #7833
Merge branch 'master' of http://darcs.haskell.org/ghc