Improve error message for missing shells
Improve error message for missing shells

Attempt to improve the missing shell error to cover the scenario when
someone is using a new style plugin but has an outdated bin/cake.php
that isn't using CommandRunner.

Refs markstory/asset_compress#324

davidyell/cakephp,cakephp/cakephp,mvdriel/cakephp,CakeDC/cakephp,ADmad/cakephp,ndm2/cakephp,davidyell/cakephp,petteyg/cakephp,ndm2/cakephp,petteyg/cakephp,dakota/cakephp,cakephp/cakephp,tenkoma/cakephp,ADmad/cakephp,tenkoma/cakephp,garethellis36/cakephp,mvdriel/cakephp,garethellis36/cakephp,tenkoma/cakephp,tenkoma/cakephp,cakephp/cakephp,davidyell/cakephp,garethellis36/cakephp,petteyg/cakephp,mvdriel/cakephp,ADmad/cakephp,CakeDC/cakephp,dakota/cakephp,dakota/cakephp,cakephp/cakephp,dakota/cakephp,ndm2/cakephp,mvdriel/cakephp,CakeDC/cakephp,CakeDC/cakephp,garethellis36/cakephp,ndm2/cakephp,ADmad/cakephp,petteyg/cakephp