all: cut bloat found in the pike audit

Dead, vestigial, and over-built code with no behavior change (except the
bool-vocabulary trim, a deliberate behavior tightening):

- httpdl: drop the vestigial sort+copy in validSegs (work-stealing was
  removed in 270812d, so segments always tile [0,total) ascending now);
  validate order in place, which also rejects a scrambled sidecar. Inline
  the endOff() accessor to s.end.
- cli: shrink the boolean vocabulary to true/false, which is all that's
  accepted. The invented yes/no/1/0/on/off spellings are gone, so e.g.
  --enable-dht=yes (or yes in got.conf) is now a usage error.
- download: remove the dead, never-called Stat.Done() method.
- progress: drop speed(), a pure alias of humanSize; call humanSize directly.
- main: replace the jobsHolder mutex box with atomic.Pointer[[]job] for the
  forced-exit session save; the capability stays, the lock and type go.
- bt: collapse isAddrInUse's X||X (missinggo.IsAddrInUse is that exact
  string match); drop the now-unused missinggo import (tidy -> indirect).
- option: note that prealloc and falloc are identical here.

progress/progress.go

@@ -147,10 +147,10 @@ func (r *Reporter) lineOne(s download.Stat) string {
 		fmt.Fprintf(&b, " SD:%d", s.Seeders)
 	}
 	if !seeding {
-		fmt.Fprintf(&b, " DL:%s", speed(dl, r.human))
+		fmt.Fprintf(&b, " DL:%s", humanSize(dl, r.human))
 	}
 	if seeding || ul > 0 {
-		fmt.Fprintf(&b, " UL:%s", speed(ul, r.human))
+		fmt.Fprintf(&b, " UL:%s", humanSize(ul, r.human))
 	}
 	if !seeding && s.Total > 0 && dl > 0 {
 		fmt.Fprintf(&b, " ETA:%s", secfmt(etaDuration(s.Total-s.Completed, dl)))
@@ -227,7 +227,7 @@ func (r *Reporter) summary(stats []download.Stat) string {
 			stalled++
 		}
 	}
-	line := fmt.Sprintf("%d active   DL:%s UL:%s", len(stats)-waiting, speed(totDL, r.human), speed(totUL, r.human))
+	line := fmt.Sprintf("%d active   DL:%s UL:%s", len(stats)-waiting, humanSize(totDL, r.human), humanSize(totUL, r.human))
 	if waiting > 0 {
 		line += fmt.Sprintf("  (%d waiting)", waiting)
 	}
@@ -254,13 +254,13 @@ func (r *Reporter) rowMetric(s download.Stat, dl, ul int64) (metric, tail string
 	case download.Waiting:
 		return "queued", ""
 	case download.Seeding:
-		return "seeding", "UL:" + speed(ul, r.human)
+		return "seeding", "UL:" + humanSize(ul, r.human)
 	case download.Complete:
 		return "done", ""
 	case download.Errored:
 		return "failed", ""
 	default:
-		metric = "DL:" + speed(dl, r.human)
+		metric = "DL:" + humanSize(dl, r.human)
 		switch {
 		case dl > 0 && s.Total > 0:
 			tail = secfmt(etaDuration(s.Total-s.Completed, dl))