[Eric] Backporting Mercurial plug-in

[Stjujsckij Nickolaj]

    Hello everyone on the list

I did some initial work on backporting Eric5 Mercurial plug-in to Eric4.
But since Eric5 is in Gentoo Portage now, I don't really need this
anymore. But if anyone does (or wants to do) the same, I could share
what's already done (local named branch in hg-clone of Eric repo).
Reply to the list if interested, would be glad to help.