Allow language names where the major mode name seems unrelated to the language

Allow language names where the major mode name seems unrelated to the language

Eric Schulte writes:

> Attached is a small patch for a small issue.
>
> Sometimes a language uses a major mode which can't be guessed
> from it's name.  This patch introduces the `org-src-lang-modes'
> variable which can be used to map language names to major modes
> when this is the case.  This is used when editing a source-code
> block, or when exporting fontified source-code with htmlize.
>
> So far the only instance of this that I know of is ocaml and
> tuareg-mode, so that's the only thing that `org-src-lang-modes'
> is pre-populated with.  Maybe there are other instances as well?