#3 fix psgml 1.2.1 for Emacs 21

[Anonymous]

Psgml uses the variables `before-change-function' and
`after-change-function', which are obsolete in GNU
Emacs 21. The following patch, by Dave Love, is
included in the Emacs 21 PROBLEMS file, but as I am
submitting an update to that patch for psgml 1.2.2, I
thought it appropriate to forward the orignal as well
and, for the sake of clarity, in a separate submission.