[PATCH 0/9] http-fetch fixes

This patch series fixes the git-http-fetch bug I reported in `git-http-fetch failure/segfault -- alas no patch'. The preliminary patch I was working on /did/ actually fix the bug I found, but uncovered a bunch more, which I think I've finally got to the bottom of.

The series applies to commit 1506fc34f7585880aeeb12b5fdfe2de4800f9df5.

Particularly: 

  1. watch-slot -- my fix for the actual bug.  Different from Nick
     Hangeval's separate-status structure, it works by locking slots
     that people still want answers from.  I've turned the in_use slot
     field into a bit mask and added a reference counter.  I think you
     can use Nick's patch instead if you prefer it.

  2, 3. list-corruption, abort-object-request -- fix bugs uncovered by
     watch-slot.  See the patch emails for the details.

  4, 5, 6, 7. multi-fdset, fix-rename-message, curl-verbose,
     par-control-flow-tidy -- various other relatively trivial changes I
     noticed while doing the main work above.  fix-rename-message is
     actually a bug, but if you think some other fix is better, that's
     cool; the others are cosmetic things.

  8, 9.  sanity-check-active-slots, sanity-check-object-queue --
     debugging code I threw in while I was trying to track down the main
     bugs.  I'm not going to cry if these aren't accepted (indeed, I
     separated them out and put them at the end specifically!) but they
     might prove useful to someone, so I thought I'd send 'em along
     anyway.

-- [mdw]