nanogui: Thread: [FLNX-0.14] Some modifications

1. FL/Fl.H
#include <config.h>
===>
#include "config.h"

2. src/Makefile
copy config.h to /usr/local/include/FL/ after make install

3. src/Makefile, configure, makeinclude.in
build a shared library

4. FL/Fl.H

delete the following lines (they're not needed):
#ifdef NANO_X  //for Nano-x,by tanghao
#define MWINCLUDECOLORS
#include "nano-X.h"
#endif //NANO_X

5. src/Fl_x.cxx

delete the folloing line(it's not needed):
#include <nxdraw.h>

6. src/fl_draw_image.cxx, FL/fl_draw.H
add the function for copying images drawn using Nano-X to FLTK:
void fl_draw_image(GR_WINDOW_ID wid, int x, int y, int w, int h,
  int srcx, int srcy)