[tex-hyphen] hyphenation with ligatures in input

[Philip Taylor]

Arthur Reutenauer wrote:

>   You should.  Characters such as U+FB01 are deprecated and shouldn't be
> used in text.

/Characters/ ... : yes.  But consider a Unicode-in/Unicode-out
preprocessor; might it not generate fi in the output stream,
since it thinks it is generating glyphs, yet in a pipeline
environment that output might get re-used as TeX input ...

** Phil.