replaced all local definitions of PI by a single one

For code maintainability, it is better to have a single definition of the
constant than many ones dispatched in many places. In addition, we try to
count on the constant M_PI that can be defined by the header <math.h> if
possible because it may have the best accuracy for the platform.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

src/wconfig.h.in

@@ -334,7 +334,6 @@
 
 /* number of window shortcuts */
 #define MAX_WINDOW_SHORTCUTS      10
-#define WM_PI                     3.14159265358979323846
 #define MIN_TITLEFONT_HEIGHT(h)   ((h)>14 ? (h) : 14)
 #define TITLEBAR_HEIGHT           18  /* window's titlebar height */
 #define RESIZEBAR_HEIGHT          8   /* height of the resizebar */