Asyncify checkout.py.  Relates to #23.
Asyncify checkout.py.  Relates to #23.

ddevlin/GitSavvy,divmain/GitSavvy,ralic/GitSavvy,asfaltboy/GitSavvy,ddevlin/GitSavvy,stoivo/GitSavvy,ypersyntelykos/GitSavvy,jmanuel1/GitSavvy,theiviaxx/GitSavvy,divmain/GitSavvy,dreki/GitSavvy,asfaltboy/GitSavvy,asfaltboy/GitSavvy,ddevlin/GitSavvy,jmanuel1/GitSavvy,dreki/GitSavvy,stoivo/GitSavvy,theiviaxx/GitSavvy,dvcrn/GitSavvy,ralic/GitSavvy,divmain/GitSavvy,stoivo/GitSavvy,ypersyntelykos/GitSavvy,dvcrn/GitSavvy