java: mraa jni library now dynamically links to libmraa

libmraajava.so was statically linking to mraa object files causing
duplicate mraa platform instances if a UPM Java module was also loaded.

JNI functionality has been moved into src/java/mraajni.c. JVM object is
now set when JVM is loaded; see updates to src/java/mraajava.i.
This was necessary as the JVM object cannot be directly referenced from
mraa as it will not be available when building C/C++ examples.

Signed-off-by: Henry Bruce <henry.bruce@intel.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

api/mraa/gpio.h

@@ -44,15 +44,8 @@ extern "C" {
 #include <Python.h>
 #endif
 
-#if defined(SWIGJAVA) || defined(JAVACALLBACK)
-#include <jni.h>
-extern JavaVM *globVM;
-extern void mraa_java_isr_callback(void *);
-#endif
-
 #include <stdio.h>
 #include <pthread.h>
-
 #include "common.h"
 
 /**

api/mraa/gpio.hpp

@@ -28,6 +28,13 @@
 #include "types.hpp"
 #include <stdexcept>
 
+#if defined(SWIGJAVA) || defined(JAVACALLBACK)
+extern "C" {
+    void mraa_java_isr_callback(void *args);
+}
+#endif
+
+
 #if defined(SWIGJAVASCRIPT)
 #if NODE_MODULE_VERSION >= 0x000D
 #include <uv.h>