Fix Android mode support  on MacOS X

The change in 2.2 to using the Oracle appbundler means that javac is no
longer available, and copying it in from outside leads to the Android
SDK utilities breaking (pre-dexing hangs, or javac hangs, or it builds
a broken Android apk that doesn't run.)

This change adds back in the javac from the JDK that Android mode needs,
and avoids breaking the Android SDK utilities in the process.