[tldoc] en-dash and em-dash ligatures in \texttt

[Karl Berry]

    about `--` versus `-{}-`, the English version still have the
    former, e.g. `\code{mtxrun --script pstopdf}`.

What I don't understand is why the dash ligatures are happening at all,
since \texttt{en--dash em---dash} in bare LaTeX doesn't create
them. Evidently some one of the many loaded packages must be changing
it, but I can't investigate in depth right now. If anyone feels like
casting their eyes over tex-live.sty and see if anything jumps out, or
doing test runs, that would be great.

I tried adding \@noligs in the definition of \code, which didn't work
because of active characters and \write expansion. And using \path didn't
work because of \url in captions. Those were all the easy workarounds I
could think of. --thanks, karl.