Loading souce Elisp faster

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

It used to be the case that compiling one's .emacs was silly because it
provided no measurable speed difference.  But nowadays this is not true
any more: loading a source Elisp file is significantly slower because it
goes through load-with-code-conversion.

For source files in utf-8 encoding this does not need to be the case: we
could load them without going through load-with-code-conversion.
And given that utf-8 should be the standard encoding for Elisp files
(if not quite now, surely in some not too distant future), this is an
important case.

So basically, all we need to do is to be able to easily recognize "Elisp
source in utf-8 encoding".  One way to do that would be to use
a BOM-like marker, e.g. start utf-8 Elisp files with "\ufeff" either at
the very beginning of the file or right after a semi-colon (for better
backward compatibility).


        Stefan