Ensure let block is not passed to super call.

Fix #820. This is directly related to bug
http://bugs.ruby-lang.org/issues/8059.  It seems to affect Ruby 1.9.3
but not Ruby 2.0.0. As per the notes, it is a heisenbug, so simply
looking at it causes the bug to disappear.

Force the call to super to make sure the let block is not passed in.
Update Changelog with issue description.
Rephrase changelog entry so it focused on the what, not the how.

[ci skip]
Clarify changelog entry.

[ci skip]
Add missing changelog entry for #808.

[ci skip]
2.13.1 release.
Don't --profile with --fail-fast and failures

i.e. don't display slow examples in the output if `--fail-fast` option
is used and there are any failures as it clutters the output.

References #730.
Make JSON formatter behave the same as text formatter

When it comes to `--profile` and `--fail-fast`.