roken: include limits.h unconditionally

Everywhere that roken is used supports limits.h.  The behavior of
roken should not depend on whether or not the including application
includes limits.h before or after roken.h.   Include limits.h in
roken.h and be done with it.

Change-Id: Id0be5487c791592dfe722ce880b8400bb16d05b1

lib/roken/roken.h.in

@@ -39,6 +39,7 @@
 #include <stdint.h>
 #endif
 #include <string.h>
+#include <limits.h>
 #include <signal.h>
 
 #ifndef ROKEN_LIB_FUNCTION