b.t.p.test_permissions : module documentation

Tests for bzr setting permissions.

Files in the branch control directory (.bzr or .bzr/branch) should inherit the .bzr directory permissions. So if the directory is group writable, the files and subdirs should be as well.

Class	TestPermissions	No class docstring; 1/3 methods documented
Class	_NullPermsStat	A class that proxy's a stat result and strips permissions.