Add a previous buffer command


git-svn-id: svn+ssh://svnrepo/projects/tachyon/trunk@7037 561c3618-0fe6-0310-b5d6-fc65c73fee30
Rename test to indicate that it only tests changing buffer in the forward
direction.


git-svn-id: svn+ssh://svnrepo/projects/tachyon/trunk@7038 561c3618-0fe6-0310-b5d6-fc65c73fee30
Add a test for the previous command


git-svn-id: svn+ssh://svnrepo/projects/tachyon/trunk@7039 561c3618-0fe6-0310-b5d6-fc65c73fee30