wmaker: Cleaned dangerous function prototype usage

- remove extern declaration in source file, use header instead

- add inclusion of header defining the functions of the file to
get the compiler to cross-check them

- marked static the functions that should not be visible ouside
their file

src/placement.c

@@ -38,6 +38,7 @@
 #include "application.h"
 #include "dock.h"
 #include "xinerama.h"
+#include "placement.h"
 
 extern WPreferences wPreferences;
 
@@ -47,10 +48,6 @@ extern WPreferences wPreferences;
 #define Y_ORIGIN WMAX(usableArea.y1,\
     wPreferences.window_place_origin.y)
 
-/* interactive window placement is in moveres.c */
-extern void InteractivePlaceWindow(WWindow *wwin, int *x_ret, int *y_ret,
-				   unsigned width, unsigned height);
-
 /* Returns True if it is an icon and is in this workspace */
 static Bool
 iconPosition(WCoreWindow *wcore, int sx1, int sy1, int sx2, int sy2,