java: Included jni.h in an external header

The reason for this is that applications that use mraa, like upm, need the
definitions contained in jni header.

Signed-off-by: Andrei Vasiliu <andrei.vasiliu@intel.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

api/mraa/gpio.h

@@ -44,6 +44,13 @@ extern "C" {
 #include <pthread.h>
 #include "common.h"
 
+#if defined(SWIGJAVA) || defined(JAVACALLBACK)
+#include <jni.h>
+extern "C" {
+    void mraa_java_isr_callback(void *args);
+}
+#endif
+
 /**
  * Opaque pointer definition to the internal struct _gpio
  */

api/mraa/gpio.hpp

@@ -28,13 +28,6 @@
 #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>

include/java/mraajni.h

@@ -28,7 +28,7 @@
 extern "C" {
 #endif
 
-#include "jni.h"
+#include <jni.h>
 #include "mraa/types.h"
 
 // location for defining JNI version to use