Add libString.

src/libString/s_nappend.c

@@ -0,0 +1,18 @@
+#include <u.h>
+#include <libc.h>
+#include "libString.h"
+
+/* append a char array ( of up to n characters) to a String */
+String *
+s_nappend(String *to, char *from, int n)
+{
+	if (to == 0)
+		to = s_new();
+	if (from == 0)
+		return to;
+	for(; n && *from; from++, n--)
+		s_putc(to, *from);
+	s_terminate(to);
+	return to;
+}
+