fix string comparison functions

builtin/string.v

@@ -169,37 +169,35 @@ fn (s string) ne(a string) bool {
 	return !s.eq(a)
 }
 
-// s >= a
-fn (s string) ge(a string) bool {
-	mut j := 0
+// s < a
+fn (s string) lt(a string) bool {
 	for i := 0; i < s.len; i++ {
-		if i >= a.len {
-			return true
-		}
-		if int(s[i]) < int(a[j]) {
+		if i >= a.len || s[i] > a[i] {
 			return false
 		}
-		else if int(s[i]) > int(a[j]) {
+		else if s[i] < a[i] {
 			return true
 		}
-		j++
 	}
-	return true
+	if s.len < a.len {
+		return true
+	}
+	return false
 }
 
 // s <= a
 fn (s string) le(a string) bool {
-	return !s.ge(a) || s == a
-}
-
-// s < a
-fn (s string) lt(a string) bool {
-	return s.le(a) && s != a
+	return s.lt(a) || s.eq(a)
 }
 
 // s > a
 fn (s string) gt(a string) bool {
-	return s.ge(a) && s != a
+	return !s.le(a)
+}
+
+// s >= a
+fn (s string) ge(a string) bool {
+	return !s.lt(a)
 }
 
 // TODO `fn (s string) + (a string)` ? To be consistent with operator overloading syntax.