[patch] fix -e signal check code

[lepton <yth...@gm...>]

See the attach patch.
We should return 0 on success.

Now the "-e signal=xxxx" won't work without this patch
(At least on the debian sarge version  4.5.8-1.2)

diff -pru strace-4.5.8/syscall.c strace-4.5.8-lepton/syscall.c
--- strace-4.5.8/syscall.c	2004-09-04 12:20:43.000000000 +0800
+++ strace-4.5.8-lepton/syscall.c	2005-08-09 17:50:03.000000000 +0800
@@ -311,10 +311,10 @@ qual_signal(s, opt, not)
 
 	if (s && *s && isdigit((unsigned char)*s)) {
 		qualify_one(atoi(s), opt, not);
-		return 1;
+		return 0;
 	}
 	if (strlen(s) >= sizeof buf)
-		return 0;
+		return -1;
 	strcpy(buf, s);
 	s = buf;
 	for (i = 0; s[i]; i++)
@@ -323,10 +323,10 @@ qual_signal(s, opt, not)
 		s += 3;
 	for (i = 0; i <= NSIG; i++)
 		if (strcmp(s, signame(i) + 3) == 0) {
-			qualify_one(atoi(s), opt, not);
-			return 1;
+			qualify_one(i, opt, not);
+			return 0;
 		}
-	return 0;
+	return -1;
 }
 
 static int