gnupg-for-java updated for GnuPG 2.x

[Robert J. Hansen]

> This should run on any platform where Java and JNI are supported, but I have
> only tested this on Android.  Patches welcome!  Be aware: it does require
> GnuPG 2.x, the passphrase handling has been remove since GnuPG 2.x handles
> passphrases via gpg-agent.

Doing a recent pull (a couple of hours ago), the build is still bombing
out due to the lack of a "context.h" file.  Is this meant to be
automatically generated, or is it missing from the source tree?