Fix regression in progress/doc backtrace output.

In 2.x it had a `#` character at the start of each line.

Also, `Failed examples` changed to `Failed Examples` recently.
This changes it back.

The output fixtures were generated from 8f7c2f45edd78c28dcc8834fda31e0f5750fde04,
before Jon's recent formatter changes.
Merge pull request #1525 from rspec/fix-formatter-regression

Fix formatter regression