Status of tests on Windows

[Dominik Ruf]

I looked into the 'flaky' tests.
The problem here is that sometimes 
(actually quite often) file handles are 
not released. I'm not sure yet if this 
doesn't happen on Linux or if it simply 
doesn't cause a problem because Linux 
allows renaming of open files.

I'm pretty sure it is dulwich that causes 
the open file handels but I'm not 100% 
sure yet.

I have seen errors about too many open 
files on Linux. Which lets me believe that 
the problem exists on Linux as well.