first aliasing feature
ExampleGroup#alias_example_group_to
rename #describe to #example_group

Conflicts:
	lib/rspec/core/example_group.rb
use new metadata interface
expose example group aliases on RSpec and globally if configured
Cleanup docs a bit.
Standardize on `__send__` over `send`.

We've occasionally received bug reports related to
users having objects that redefine `send` (e.g.
`Email#send`), and using `__send__` is best to avoid
those problems.

Many of the receivers of `__send__` here are objects
we own and that do not (and never will) redefine `send`;
however, for consistency, it's good to standardize on
`__send__`. That way, we're less likely to forget it in
the future for a case where it does matter.
Add missing spec.

This already worked but wasn't covered by a test.
Improve DSL specs.

- Cover all the edge cases.
- Use a subprocess for global config changes.
- No need to use a separate example group per method.
  It adds to the runtime of the test suite with no benefit.
Ensure example group aliases are exposed globally if so configured.

Before, they were not exposed globally if the config option
was already set.
Cleanup how the DSL is defined.

- No need to use send.
- Extract change_global_dsl helper method.
Update ignored method cache busters.
Fix invalid 1.8.7 syntax.
Fix `expose_globally` reader.

- Make it a predicate w/ a question mark.
- Make it actually indicate if the DSL is exposed globally.
Remove `example_group` from top level DSL.

We don't need to expose it at the top level, and
it's best to cut down on what's exposed.
Refactor: use `alias_example_group_to` to define example group aliases.
Add additional example group aliases.
Update aliasing cuke.
Add docs for `alias_example_group_to`.
Update changelog.