Upstream merge

I'm happy to inform you that the patching is done :) Now the new Android class path version seems to work along with Avian on Windows 7, OS X and Linux. There could be bugs (just as always), but we did some basic testing and nothing critical is found.

But unfortunately this pull request contains only a part (the major part) of the changes. We had to make some changes in two other repositories. One of them is Avian itself (pull request https://github.com/ReadyTalk/avian/pull/343). And the other one is the new conscrypt repo. The changes are made in my fork as a part of avian-pack. The conscrypt repo itself is here: https://github.com/bigfatbrowncat/avian-pack.android.external.conscrypt

You may fork this repo as well as you forked libcore. If it's not a good idea, please, let us know.

By the way: the current version of avian-pack builds with all the correct versions of the repositories (you can see them in my GitHub account. Their names start with "avian-pack.")