Fix for bug #1145 bevel numbutton not changing when clicking on the sides

http://projects.blender.org/tracker/index.php?func=detail&aid=1145&group_id=9&atid=125

I changed the fbutton function to give the possibility to control the a1 and a2 parameters of the button.

This commit also fixes two things in the bevel function:
- The numbut didn't do anything because it wasn't recalculating the proper variable
- The display wasn't recalculated when pressing Ctrl or Shift (it's now done by recalculating after every keyboard event. I've done it this way since the event loops seems to skip CTRL and SHIFT events)

source/blender/include/BIF_toolbox.h

@@ -113,7 +113,7 @@ int saveover (char *filename);
 int okee (char *fmt, ...);
 
 short button (short *var, short min, short max, char *str);
-short fbutton (float *var, float min, float max, char *str);
+short fbutton (float *var, float min, float max, float a1, float a2, char *str);
 short sbutton (char *var, float min, float max, char *str);	/* __NLA */
 int movetolayer_buts (unsigned int *lay);
 void draw_numbuts_tip (char *str, int x1, int y1, int x2, int y2);