Fix two incall activities instances when receiving a call

src/org/linphone/IncallActivity.java

@@ -152,7 +152,7 @@ public class IncallActivity extends AbstractCalleesActivity implements
 	
 	@Override
 	protected void onPause() {
-		IncallActivity.active = false;
+		setActive(false);
 		super.onPause();
 	}
 

src/org/linphone/LinphoneActivity.java

@@ -422,9 +422,10 @@ public class LinphoneActivity extends TabActivity implements ContactPicked
 		}
 		mHandler.post(new Runnable() {
 			public void run() {
-				if (IncallActivity.instance() != null && IncallActivity.instance().isActive()) return;
+				if (IncallActivity.active) return;
 				Intent intent = new Intent().setClass(LinphoneActivity.this, IncallActivity.class);
 				startActivityForResult(intent, incall_activity);
+				IncallActivity.active = true;
 			}
 		});
 	}