Add spec for backwardsScan.
Add spec for backwardsScan.

mizchi-sandbox/standalone-atom-editor,whodatninja/text-buffer,jacekkopecky/text-buffer,atom/text-buffer,mizchi-sandbox/standalone-atom-editor,jacekkopecky/text-buffer,pombredanne/text-buffer,pombredanne/text-buffer,atom/text-buffer