Bug 700429: Limit size of input regular expression program.

The size of the parsed syntax list could overflow. Allowing it to be
bigger than the compiled program makes no sense, so use the same size
limit when parsing as when compiling.

regexp.c

@@ -836,6 +836,8 @@ Reprog *regcompx(void *(*alloc)(void *ctx, void *p, int n), void *ctx,
 	if (!g.prog)
 		die(&g, "cannot allocate regular expression");
 	n = strlen(pattern) * 2;
+	if (n > MAXPROG)
+		die(&g, "program too large");
 	if (n > 0) {
 		g.pstart = g.pend = alloc(ctx, NULL, sizeof (Renode) * n);
 		if (!g.pstart)