Allow strings longer than 256 bytes

Use an int rather than a char for counting.

Thanks to Thierry for the diagnosis.

Fixes #896

bin/varnishtest/tests/r00896.vtc

+test "Ticket #896, strings over 256 bytes"
+
+server s1 {
+	rxreq 
+	txresp
+} -start
+
+varnish v1 -vcl+backend {
+	sub vcl_recv {
+	    if (req.http.host ~ "^(abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij|abcdefghij)") {
+		error 500 "not ok";
+		}
+	}
+} -start 
+
+client c1 {
+	txreq  
+	rxresp
+	expect resp.status == 200
+} -run

lib/libvcl/vcc_token.c

@@ -350,7 +350,7 @@ static int
 vcc_decstr(struct vcc *tl)
 {
 	char *q;
-	unsigned char l;
+	unsigned int l;
 
 	assert(tl->t->tok == CSTR);
 	l = (tl->t->e - tl->t->b) - 2;