Android: Implement open and save file dialog.

Android.mk

@@ -30,6 +30,8 @@ LOCAL_SRC_FILES := \
 	$(wildcard $(LOCAL_PATH)/src/core/*.c) \
 	$(wildcard $(LOCAL_PATH)/src/core/android/*.c) \
 	$(wildcard $(LOCAL_PATH)/src/cpuinfo/*.c) \
+    $(LOCAL_PATH)/src/dialog/SDL_dialog_utils.c \
+    $(LOCAL_PATH)/src/dialog/android/SDL_androiddialog.c \
 	$(wildcard $(LOCAL_PATH)/src/dynapi/*.c) \
 	$(wildcard $(LOCAL_PATH)/src/events/*.c) \
 	$(wildcard $(LOCAL_PATH)/src/file/*.c) \