Merge branch 'android-app'

This branch introduces a userland IPsec implementation (libipsec) and an
Android App which targets the VpnService API that is provided by Android 4+.

The implementation is based on the bachelor thesis 'Userland IPsec for
Android 4' by Giuliano Grassi and Ralf Sager.

diff --cc configure.in
Simple merge

diff --cc src/libcharon/Makefile.am
Simple merge

diff --cc src/libstrongswan/printf_hook.h
Simple merge