Fix Core pretty printer
Fix Core pretty printer

If a JoinId (bogusly) ends up in an argument position we printed
    f jump j
rather than
    f (jump j)

Easy to fix.

sdiehl/ghc,ezyang/ghc,shlevy/ghc,sdiehl/ghc,shlevy/ghc,ezyang/ghc,ezyang/ghc,shlevy/ghc,shlevy/ghc,sdiehl/ghc,ezyang/ghc,shlevy/ghc,shlevy/ghc,ezyang/ghc,shlevy/ghc,ezyang/ghc,sdiehl/ghc,sdiehl/ghc,ezyang/ghc,sdiehl/ghc,sdiehl/ghc