Avoid Data.List.init and Data.List.last

[Bodigrim]

Once haskell/core-libraries-committee#292 is implemented,

parsec/src/Text/Parsec/Error.hs

Lines 217 to 219 in e5fd658

	commasOr [] = ""
	commasOr [m] = m
	commasOr ms = commaSep (init ms) ++ " " ++ msgOr ++ " " ++ last ms

will raise a warning.

Not urgent and not a blocker (I can relax warning settings in Hadrian to pass GHC build), just heads up. Happy to prepare a patch, if it helps.