all: reword comments to state behavior directly

Comments (and one test comment) now describe the rules on their own terms
instead of by comparison to another downloader. No behavior change.

cli/parse_test.go

@@ -139,8 +139,8 @@ func TestValidateFloatNonNegative(t *testing.T) {
 
 func TestValidateBool(t *testing.T) {
 	b := byLong["enable-dht"]
-	// aria2 accepts only literal true/false (case-sensitive) but trims
-	// surrounding whitespace; match that exactly.
+	// Only literal true/false are accepted (case-sensitive), with surrounding
+	// whitespace trimmed.
 	for _, ok := range []string{"true", "false", " true ", "false\t"} {
 		if err := validate(b, ok); err != nil {
 			t.Errorf("validate bool %q: %v", ok, err)