Deprecation warning when RSpec.run is programmatically invoked twice.

This is because RSpec.reset is no longer called for users as of RSpec
3.0.0 so this deprecation warning will indicate to them that the need to
invoke the method themselves.
Merge pull request #1579 from rspec/deprecate-run-auto-reset

Print a deprecation about reset when RSpec.run is called twice.
Simplify warning/tests for reset deprecation

Conflicts:
	lib/rspec/core.rb
	spec/command_line/order_spec.rb
	spec/rspec/core/runner_spec.rb
Add a full changelog entry for #1587.

Conflicts:
	Changelog.md
Merge pull request #1587 from rspec/1579-cleanup

1579 cleanup
raise errors for deprecations
move generation of description to prevent issue with doubles with inline should