Constify the argument of wstrdup()

WINGs/WINGs/WUtil.h

@@ -245,7 +245,7 @@ void wfree(void *ptr);
 void wrelease(void *ptr);
 void* wretain(void *ptr);
 
-char* wstrdup(char *str);
+char *wstrdup(const char *str);
 char* wstrndup(char *str, size_t len);
 
 /* Concatenate str1 with str2 and return that in a newly malloc'ed string.

WINGs/string.c

@@ -163,7 +163,7 @@ char *wtrimspace(char *s)
 	return c;
 }
 
-char *wstrdup(char *str)
+char *wstrdup(const char *str)
 {
 	assert(str != NULL);