Prevent unnecessary compilation due to changes in plot_common.h.

The header plot_common.h was included in basic_gal.h which was not
required for compilation.  Remove the plot_common.h include to prevent
large swaths of KiCad from being recompiled when the plot_common.h is
changed.

include/basic_gal.h

@@ -2,7 +2,7 @@
  * This program source code file is part of KiCad, a free EDA CAD application.
  *
  * Copyright (C) 2016 Jean-Pierre Charras, jp.charras at wanadoo.fr
- * Copyright (C) 1992-2016 KiCad Developers, see AUTHORS.txt for contributors.
+ * Copyright (C) 1992-2017 KiCad Developers, see AUTHORS.txt for contributors.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -25,13 +25,15 @@
 #ifndef BASIC_GAL_H
 #define BASIC_GAL_H
 
-#include <plot_common.h>
 #include <class_eda_rect.h>
 
 #include <gal/stroke_font.h>
 #include <gal/graphics_abstraction_layer.h>
 #include <newstroke_font.h>
 
+class PLOTTER;
+
+
 /*
  * class BASIC_GAL is a minimal GAL implementation to draw, plot and convert
  * stroke texts to a set of segments for DRC tests, and to calculate text sizes.