index: GetDirMembers, forgot to close iterator

Could fix too many open files problem with sqlite reported by ajft

Change-Id: Icde85b11dcd96a336d1bba1e15a7665a1b4a874a
Move pkg/gate to pkg/syncutil, to house more stuff.

Change-Id: I737458641a9de03da55ed627bfac10f3377a13aa
Merge branch 'master' of https://camlistore.googlesource.com/camlistore
Add syncutil.Group: an easy way to do multiple things at once.

Change-Id: Ie28885a5f42019dd1c3fb14f92c7cc5d40e08742
Do directory describe queries in parallel.

Change-Id: I9e3a4d97a97b177356d11d4ff0a735d80bfc63db
TODO: use syncutil.Group in many more places.