astropy.log: The process cannot access the file because it is being used by another process

`c:\windows\temp\tmpyzcvmqastropy_config\astropy\astropy.log: The process cannot access the file because it is being used by another process`

This is an error I get sometimes when the tests are run in Windows on Jenkins.  Right now this is only happening in my staging branch where I'm testing #495, though I'd like to merge that work.

It always happens at the exact same point in the tests.  To give a little further context:

```
astropy\io\fits\tests\test_image.py:883: TestImageFunctions.test_scale_back PASSED
astropy\io\fits\tests\test_image.py:907: TestImageFunctions.test_scale_back_compressed PASSED
astropy\io\fits\tests\test_image.py:948: TestImageFunctions.test_insufficient_compression_allocation error: c:\windows\temp\tmpyzcvmqastropy_config\astropy\astropy.log: The process cannot access the file because it is being used by another process

E:\Builds\astropy-winxp32-staging-iguananaut\workspaces\COMPILER\mingw32\NUMPY_VER\numpy-1.5.1\PYTHON_VER\python-2.7>exit 1 
```

It seems like the test runner itself is crashing, because the tests just stop there.  The test it's stopping at is a slightly bizarre one, but it doesn't do anything I can think of that would affect the log, so I'm not convinced the test itself is relevant (though I might try disabling it).  This occurs on some test configurations but not others, though I haven't discerned any pattern so I think it's more or less non-deterministic.  When I run the tests manually in the same configuration it does not occur, so it seems like it might be due to an interaction with Jenkins.

Any hypotheses?