WUtil: Added 'const' attribute on non-modified arguments to functions

A number of functions do not actually modify the strings given as
parameter, but only read or duplicate it. In this case it is a good
practice to mark that parameter as pointer-to-const to let the
compiler known about it, to be able to perform appropriate
optimisations.

WINGs/userdefaults.c

@@ -80,7 +80,7 @@ char *wusergnusteppath()
 	return path;
 }
 
-char *wdefaultspathfordomain(char *domain)
+char *wdefaultspathfordomain(const char *domain)
 {
 	char *path;
 	char *gspath;