Remove dup code from getWindowMakerIconImage()

The code to find the icon in the function getWindowMakerIconImage()
is duplicated, because it is the same code as in get_default_icon_filename()

This patch includes the prototypes of get_default_icon_filename()
and get_default_icon_rimage() in defaults.h, so these functions
can be used in other files.

src/defaults.h

@@ -48,4 +48,7 @@ RImage * wDefaultGetImage(WScreen *scr, char *winstance, char *wclass, int max_s
 
 int wDefaultGetStartWorkspace(WScreen *scr, char *instance, char *class);
 void wDefaultChangeIcon(WScreen *scr, char *instance, char* class, char *file);
+char *get_default_icon_filename(WScreen *scr, char *winstance, char *wclass, char *command,
+				Bool noDefault);
+RImage *get_default_icon_rimage(WScreen *scr, char *file_name, int max_size);
 #endif /* WMDEFAULTS_H_ */