[MERGE] Cleanup and test Lock objects

[Alexander Belchenko]

Alexander Belchenko has voted +1 (conditional).
Status is now: Conditionally approved
Comment:
I'd like to suggest to remove dependency on win32con module: it's very 
bloat, and for ctypes path of code you anyway provide required constants 
manually.
This will help to shrink our standalone bzr.exe a bit.

I also want to have test for situation as in test_dirstate.py: 
test_initialize when the test code try to obtain lock, and then open the 
locked file again to read. Or we can just switch that test to use 
lock_obj.f.read() ?

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C45F731B8.2000603%40arbash-meinel.com%3E