When locking a file on windows, EACCESS tells us we have it locked already, not EDEADLOCK
Bug noticed by mobmix on #tor, msdn description on http://msdn.microsoft.com/en-us/library/8054ew2f(v=vs.80).aspx
remaining question I want to answer for myself is what happens when we already hold the lock and try to blockingly lock it again (do we get EACCESS like I hope or do we get EDEADLOCK)
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