Fix up prototype of strtoul() to match POSIX.

src/core/misc.c

 	return 0;
 }
 
-unsigned long strtoul(const char *p, const char **endp, int base)
+unsigned long strtoul(const char *p, char **endp, int base)
 {
 	unsigned long ret = 0;
 	if (base != 10) return 0;

src/include/stdlib.h

 #ifndef STDLIB_H
 #define STDLIB_H
 
-extern unsigned long strtoul ( const char *p, const char **endp, int base );
+extern unsigned long strtoul ( const char *p, char **endp, int base );
 
 #endif /* STDLIB_H */