bug#7346: `load-file-name' undocumented

[MON KEY]

Despite it being exceedingly useful, I'm unable to find reference/documentation
of the `load-file-name' variable in the manuals.

It is quite unfortunate that this particular feature hasn't been better
advertised to users.

AFAICT Emacs 23.2 lisp reference manual does not provide any documentation of
this variable.

This said, as of Bzr-102222 `load-file-file-name' is passingly
referenced by lisp
manual in /doc/lispref/package.texi

Other than that, its only other appearance is in a lisp example in
/doc/misc/viper.texi

Future manuals should provide discussion of this variable in at least one other
location _other than_ w/re packages.

At very least, the documentation of Emacs' Vi compatibility should not be given
to appear more knowledgeable about this feature than the Emacs lisp manual!

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/s_P\