rework spec to harness output correctly
allow override of runner output
Swap output stream to current sandbox (Read why).

Specs that use the runner need to use the current sandbox output stream
(rather than attempting to create a new one) so that inadvertant use of
the config hasn't preloaded any formatters (e.g. deprecation warnings
will cause stuff to be initialised which would then not be captured in
our specs correctly).
revert overwriting output and fixup spec to discourage it
Merge pull request #1073 from rspec/fix_formatter_output_issue

Running rspec-core's specs with `--order default` produces an error
Remove RSpec 1 load error handling.
Merge pull request #1074 from rspec/remove_rspec_1_error

Remove RSpec 1 load error handling.
Fix YARD docs for config macros.

These config attributes weren't rendering
in the YARD API docs before.
Error rather than warn when `let` accessed in :all hook.
Merge pull request #1078 from rspec/disallow_let_from_before_all

Error rather than warn when `let` accessed in :all hook.
Test against the other rspec gems in the ci build.
Add a print to help testing this build against other gems thing.
Delete debugging test print.
Use `-fp -b` when running against the other gems.
Executing cucubmer is a good thing, let's do that.
Recommended approach for finding and verifying code that invalidates the
message cache.
Merge pull request #1082 from xaviershay/issue-863

Recommended approach for finding and verifying code that invalidates the message cache.
Clean up BacktraceCleaner

The global configuration object exposes exclusion_patterns,
inclusion_patterns, and full_backtrace for modification at any time
during a run. This means that it would be perfectly reasonable for a
user to turn full_backtrace on and off around specific examples, and
also change the content of each patterns array at any time.

This commit does a number of things:

* clarifies examples
* decouples full_backtrace from exclusion_patterns
* makes it so that setting full_backtrace true or false
  preserves the content of exclusion_patterns and inclusion_patterns.
* simplifies the constructor
  * no args (no code outside examples submitted args to constructor)
* simplifies default backtrace inclusion patterns
  * consistent default regardless of exclusion patterns
    * eliminates order dependency of assignments
    * does not conflict with behavior of keeping anything in working
      directory by default
* simplifies the format_backtrace helper
  * collapses it into (effectively) piped iterators
  * see benchmarks/index_v_take_while.rb
remove spec_helper from default backtrace exclusions

Also moved examples for backtrace cleaner defaults to backtrace cleaner
spec (from configuration spec).
use a guard to clarify the decoupling of in/exclusion patterns from full_backtrace