[errors] Remove Fix(), move MultiErrorFromErrors().

common/sync/parallel/workPool.go

Index: common/sync/parallel/workPool.go
diff --git a/common/sync/parallel/workPool.go b/common/sync/parallel/workPool.go
index b1592b068271eff2168e0954e1d5c28f9d456281..05c01e0a8f41cf64f2796114583354cddfc16341 100644
--- a/common/sync/parallel/workPool.go
+++ b/common/sync/parallel/workPool.go
@@ -17,7 +17,7 @@ import (
 // WorkPool blocks until all the generator completes and all workers have
 // finished their tasks.
 func WorkPool(workers int, gen func(chan<- func() error)) error {
-	return errors.MultiErrorFromErrors(Run(workers, gen))
+	return multiErrorFromErrors(Run(workers, gen))
 }
 
 // FanOutIn is useful to quickly parallelize a group of tasks.
@@ -34,3 +34,23 @@ func WorkPool(workers int, gen func(chan<- func() error)) error {
 func FanOutIn(gen func(chan<- func() error)) error {
 	return WorkPool(0, gen)
 }
+
+// multiErrorFromErrors takes an error-channel, blocks on it, and returns
+// a MultiError for any errors pushed to it over the channel, or nil if
+// all the errors were nil.
+func multiErrorFromErrors(ch <-chan error) error {
+	if ch == nil {
+		return nil
+	}
+	ret := errors.MultiError(nil)
+	for e := range ch {
+		if e == nil {
+			continue
+		}
+		ret = append(ret, e)
+	}
+	if len(ret) == 0 {
+		return nil
+	}
+	return ret
+}