Node._service_startup_failed should not call os.abort()

[daira]

Running tests on Windows:

    test_upload_and_download_random_key ... Node._startService failed, aborting
[Failure instance: Traceback: <type 'exceptions.WindowsError'>:
 [Error 32] The process cannot access the file because it is being used by another process
C:\Python27\lib\site-packages\twisted-12.2.0-py2.7-win32.egg\twisted\internet\base.py:1178:mainLoop
C:\Python27\lib\site-packages\twisted-12.2.0-py2.7-win32.egg\twisted\internet\base.py:773:runUntilCurrent
C:\Python27\lib\site-packages\twisted-12.2.0-py2.7-win32.egg\twisted\internet\defer.py:368:callback
C:\Python27\lib\site-packages\twisted-12.2.0-py2.7-win32.egg\twisted\internet\defer.py:464:_startRunCallbacks
--- <exception caught here> ---
C:\Python27\lib\site-packages\twisted-12.2.0-py2.7-win32.egg\twisted\internet\defer.py:551:_runCallbacks
c:\tahoe\git\trunk\src\allmydata\node.py:379:_setup_tub
c:\tahoe\git\trunk\src\allmydata\util\fileutil.py:256:write_atomically
c:\tahoe\git\trunk\src\allmydata\util\fileutil.py:248:move_into_place
]
calling os.abort()

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.

Calling os.abort breaks testing because it terminates the whole test process, when actually just that test should fail.

[exarkun]

The os.abort call was removed in ffc2f48cfeecd5c9615ddc3b116cd2d6d1d431ce