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/options.go

@@ -27,9 +27,8 @@ func (o *Options) IsSet(name string) bool { return o.set[name] }
 // Str returns the raw string value (empty if unset and no default).
 func (o *Options) Str(name string) string { return o.vals[name] }
 
-// boolWords is the accepted vocabulary for boolean options. aria2 takes only
-// true/false (and rejects everything else), so we match it rather than inventing
-// extra spellings. boolWord is the single consult point — the Bool reader,
+// boolWords is the accepted vocabulary for boolean options: exactly true and
+// false, nothing else. boolWord is the single consult point — the Bool reader,
 // validate(), and the no-conf bootstrap all go through it — so exactly the words
 // that validate are honoured.
 var boolWords = map[string]bool{
@@ -38,9 +37,8 @@ var boolWords = map[string]bool{
 }
 
 // boolWord reports a value's truth and whether it is a recognised boolean word.
-// Whitespace is trimmed (aria2 strips config values too), but case is
-// significant: aria2 rejects "True"/"TRUE", so the match is against exactly
-// "true"/"false".
+// Whitespace is trimmed, but case is significant: "True"/"TRUE" are rejected, so
+// the match is against exactly "true"/"false".
 func boolWord(s string) (val, ok bool) {
 	val, ok = boolWords[strings.TrimSpace(s)]
 	return val, ok