Fix ServerShell not being able to handle plugin assets.
Fix ServerShell not being able to handle plugin assets.

Fixes #3575


	See: cakephp/cakephp@410981296cf916c8f27eb2ac3489004a8031a1ef


QoboLtd/project-template-cakephp,makallio85/fish-diary,QoboLtd/project-template-cakephp,makallio85/fish-diary,QoboLtd/project-template-cakephp,QoboLtd/project-template-cakephp,makallio85/fish-diary,QoboLtd/project-template-cakephp,ojengwa/cake-appengine,ojengwa/cake-appengine