* texinfo.tex (\inforef): Move to more appropriate place.
(\pounds): Remove spurious extra $.
(\email): Typeset argument in angle brackets.
(\macro): Use \doignore for robustness, instead of just letting TeX
parse the argument.
(\unmacro): Define.
actually center.
(\unnchfplain): Just call \chfplain.
(\chfplain): Rewrite to be generally callable.
(\centerparametersmaybe): Hook, a no-op except with @centerchap.
* texinfo.tex (\heading, \subheading, \subsubheading): Can no
longer call the nonexistent \*secheadingi series. Instead, call
\plain*secheading.
(\plainsubsecheading, \plainsubsubsecheading): New macros, by analogy
with \plainsecheading.
(\unnumberedsubseczzz, \unnumberedsubsubseczzz): Call them.
