JNI: Initial commit of C wrapper functions

If the user runs "configure --with-java", a separate library is built
with Java native interface stubs and it can be loaded with:

    System.loadLibrary("openconnect-wrapper");

On a native build, it should autodetect the jni.h location by looking at
JAVA_HOME or the path to javac.  On a cross build,
--with-java=/java_home/include must be explicitly specified.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
JNI: Initial commit of Java library + example program

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Enable JNI in build

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Add libstoken to build

This was tested with NDK release r8e on ARM (on a real device) and
x86 (compile only).

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Add liboath to build

Compile-tested with NDK r9:

    make NDK=/opt/android-ndk-r9 GCCVER=4.8

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
android: Add "sources" target

Provide an easy way to download and extract the source tarballs in
anticipation of a multiplatform build.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
main: Add --timestamp option

This is useful for debugging connection timeouts and DPD/Keepalive
problems.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>