HexPrec.hs		Uses hexadecimal notation to specify precedence of infix operator. We don't retain that info.
RealGHC.lhs		Literate haskell.
SpecializeInstance.hs	Prints SPECIALISE instead of SPECIALIZE.
Unicode.hs		Printing is not Unicode-aware.
UnicodeSyntax.hs	Printing is not Unicode-aware.
QuasiQuoteOld.hs	Exact printer always uses new quasi-quote syntax.