bug#7665: Emacs: add command line option -L to set more paths toload-path

[Drew Adams]

> To use and test packages outside of standard Emacs installation
> directories, it would be nice to have option -L (like in linkers) to
> prepend paths easily to load-path.
> 
> An example:
> 
>  emacs -L ~/elisp/package -L ~/.emacs.d/downloaded -l my-test.el
> 
> The long version of the option could be names:
> 
>  --load-path

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