forbidding user defined macro names of texinfo @-commands

[Patrice Dumas]

Hello,

For many @-commands, letting users redefine them should be harmless.  But
I think that we should forbid redefinition of some @-commands, or at
least issue a warning. 

Here is a list of @-commands I think should be forbidden either because
they are building blocks of the language, or because they change how
the source is interpreted:

alias, appendix*, bye, c, chapter, comment, clear, clickstyle, docbook,
documentencoding, documentlanguage, html, hyphenation, if*, ignore, 
include, macro, node, section, set, tex, top, unmacro, unnumbered*, 
value, verb, verbatim, verbatiminclude

Opinions?

-- 
Pat