Synchronize `rspec spec` and `rake spec` output

By removing the `rake spec` short circuiting the output between
invocation methods matches more closely.

Fixes rspec/rspec-core#812
added failing spec for calling #let w/o a block
Give a useful error when let or subject called without a block.

This is done by nil chcking the block in let before using it.

Signed-off-by: Sam Phippen <samphippen@googlemail.com>
Changelog entry for new subject/let error messages

Signed-off-by: Sam Phippen <samphippen@googlemail.com>
Merge pull request #838 from sorentwo/sync-rake-spec-output

Synchronize `rspec spec` and `rake spec` output
Unify "run everything" cukes and clarify usage

This collapses the descriptions of both former
run_everything_when_everything_filtered features. Additionally it adds
a scenario showing that the setting only applies to inclusion filters,
not exclusion filters.
Merge pull request #860 from sorentwo/unify-run-all-cukes

Unify "run everything" cukes and clarify usage
Merge pull request #859 from samphippen/let-without-a-block

Give a better error message when let called without a block.
describe behaviour of how shared examples behave in contexts
remove shared examples from world
move to talking to shared examples directly rather than on world
shared examples should be declared on the group they're used on, as they are now context specific
refactor specs so that shared_examples are declared in context
use correct spacing