[PATCH 0/7] fix transfer.hiderefs with smart http

I'm experimenting with using transfer.hiderefs on a server, and it's rather easy to cause a git client to hang when fetching from such a repo over smart http. Details are in the first patch.

There are 7 patches here, but the entirety of the fix is contained in the first one. The rest are cleanups and test enhancements I found along the way. I moved the fix to the front of the series as we probably want it to go to "maint", but the others can wait (being mostly test modifications, they should not cause regressions, but they'd possibly want more cooking time in case I broke the test suite for somebody).

The patches are:

  [1/7]: upload-pack: fix transfer.hiderefs over smart-http

    The fix.

  [2/7]: upload-pack: do not check NULL return of lookup_unknown_object

    A nearby cleanup.

  [3/7]: t: translate SIGINT to an exit
  [4/7]: t: redirect stderr GIT_TRACE to descriptor 4
  [5/7]: t: pass GIT_TRACE through Apache

    These all solve irritations I had when trying to debug the test.

  [6/7]: t5541: move run_with_cmdline_limit to test-lib.sh
  [7/7]: t5551: make EXPENSIVE test cheaper

    I had thought at first that the problem was related to large http
    fetches, but it turned out not to be. But I think these cleanups
    are a good thing, as they increase the default test coverage.

-Peff