Problems with pickier javah in JDK 1.7, that was occasionally causing a build failure.

compile-native-host:
     [exec] /opt/jdk1.7.0/bin/javah -force -o ../prism-es2-native/build/com_sun_prism_opengl_impl_gl2_GL2Impl$ARBVBOKey.h -jni -classpath ../prism-es2/build/classes com.sun.prism.opengl.impl.gl2.GL2Impl$ARBVBOKey
     [exec] /opt/jdk1.7.0/bin/javah -force -o ../prism-es2-native/build/com_sun_prism_opengl_impl_x11_glx_X11ExternalGLXContext.h -jni -classpath ../prism-es2-x11/build/classes com.sun.prism.opengl.impl.x11.glx.X11ExternalGLXContext
     [exec] Error: cannot access com.sun.prism.opengl.impl.GLContextImpl
     [exec] class file for com.sun.prism.opengl.impl.GLContextImpl not found
     [exec] make: *** [../prism-es2-native/build/com_sun_prism_opengl_impl_x11_glx_X11ExternalGLXContext.h] Error 1

Note that I did not always see the build failure on Linux, but this sequence would hit it every time:

# after a clean top level build
cd rt-closed/prism-es2-native
make clean
cd ../prism-es2
ant