obsync: fix behavior when run without arguments
obsync: proper calls to higher Store.__init__ methods
obsync: fix potential problems with use of sobj

Fix one place where sobj should have been changed to obj and two places
where if an exception is thrown at a bad time, sobj would not be defined
during processing of the exception.
git: add vim swap files to .gitignore
obsync: fix error handling during test_xattr_support