fix serious bug in strchr - char signedness

search for bytes with high bit set was giving (potentially dangerous)
wrong results. i've tested, cleaned up, and hopefully sped up this
function now.

src/string/strchr.c

@@ -10,14 +10,16 @@
 
 char *strchr(const char *s, int c)
 {
-	c = (char)c;
+	size_t *w, k;
+
+	c = (unsigned char)c;
 	if (!c) return (char *)s + strlen(s);
-	for (; ((uintptr_t)s & ALIGN) && *s && *s != c; s++);
-	if (*s && *s != c) {
-		const size_t *w;
-		size_t k = ONES * c;
-		for (w = (const void *)s; !HASZERO(*w) && !HASZERO(*w^k); w++);
-		for (s = (const void *)w; *s && *s != c; s++);
-	}
-	return *s ? (char *)s : 0;
+
+	for (; ((uintptr_t)s & ALIGN) && *s; s++)
+		if (*(unsigned char *)s == c) return (char *)s;
+	k = ONES * c;
+	for (w = (void *)s; !HASZERO(*w) && !HASZERO(*w^k); w++);
+	for (s = (void *)w; *s; s++)
+		if (*(unsigned char *)s == c) return (char *)s;
+	return 0;
 }