bug#6915: Please consider making left-margin-width etc buffer local instead of major mode local

[Stefan Monnier <monnier@iro.umontreal.ca>]

> To me it looks like it is more likely that it is used as a buffer
> local variable (cf linum-mode for example) than a major mode local
> variable.

You might be right: it affects the whole buffer in a uniform way, so
clearly for a multi-major mode buffer, it's not specific to a particular
major mode.

Seeing how it's a little-used variable, and how it's easier to ignore the
permanent-local property on a case-by-case basis than to add it on
a case-by-case basis (which means that most vars should be
permanent-local until it's shown they shouldn't be, rather than the
current reverse situation), I'm in favor of such a change.


        Stefan