Upgrade Android build to Gradle build system

The old Ant build system has been deprecated for a while and new development is focused on Gradle.
I also removed a hardcoded string that lint caught and moved the patch files to a subdirectory.
I left the JNI files in the root directory.

build/android/src/main/java/net.minetest.minetest/MtNativeActivity.java

@@ -0,0 +1,100 @@
+package net.minetest.minetest;
+
+import android.app.NativeActivity;
+import android.content.Intent;
+import android.os.Bundle;
+import android.util.Log;
+import android.view.WindowManager;
+
+public class MtNativeActivity extends NativeActivity {
+	@Override
+	public void onCreate(Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		m_MessagReturnCode = -1;
+		m_MessageReturnValue = "";
+
+	}
+
+	@Override
+	public void onDestroy() {
+		super.onDestroy();
+	}
+
+
+	public void copyAssets() {
+		Intent intent = new Intent(this, MinetestAssetCopy.class);
+		startActivity(intent);
+	}
+
+	public void showDialog(String acceptButton, String hint, String current,
+			int editType) {
+
+		Intent intent = new Intent(this, MinetestTextEntry.class);
+		Bundle params = new Bundle();
+		params.putString("acceptButton", acceptButton);
+		params.putString("hint", hint);
+		params.putString("current", current);
+		params.putInt("editType", editType);
+		intent.putExtras(params);
+		startActivityForResult(intent, 101);
+		m_MessageReturnValue = "";
+		m_MessagReturnCode   = -1;
+	}
+
+	public static native void putMessageBoxResult(String text);
+
+	/* ugly code to workaround putMessageBoxResult not beeing found */
+	public int getDialogState() {
+		return m_MessagReturnCode;
+	}
+
+	public String getDialogValue() {
+		m_MessagReturnCode = -1;
+		return m_MessageReturnValue;
+	}
+
+	public float getDensity() {
+		return getResources().getDisplayMetrics().density;
+	}
+
+	public int getDisplayWidth() {
+		return getResources().getDisplayMetrics().widthPixels;
+	}
+
+	public int getDisplayHeight() {
+		return getResources().getDisplayMetrics().heightPixels;
+	}
+
+	@Override
+	protected void onActivityResult(int requestCode, int resultCode,
+			Intent data) {
+		if (requestCode == 101) {
+			if (resultCode == RESULT_OK) {
+				String text = data.getStringExtra("text");
+				m_MessagReturnCode = 0;
+				m_MessageReturnValue = text;
+			}
+			else {
+				m_MessagReturnCode = 1;
+			}
+		}
+	}
+
+	static {
+		System.loadLibrary("openal");
+		System.loadLibrary("ogg");
+		System.loadLibrary("vorbis");
+		System.loadLibrary("ssl");
+		System.loadLibrary("crypto");
+		System.loadLibrary("gmp");
+		System.loadLibrary("iconv");
+
+		// We don't have to load libminetest.so ourselves,
+		// but if we do, we get nicer logcat errors when
+		// loading fails.
+		System.loadLibrary("minetest");
+	}
+
+	private int m_MessagReturnCode;
+	private String m_MessageReturnValue;
+}