Revert changes made to Engine.pm in 1ef7eeb (5.90070)

In 1ef7eeb ("removed old PSGI Engine backcompat ") some back compat code
was removed from lib/Catalyst/Engine.pm. But, this backcompat code is
apparently still needed and being used out in the wild.

This breaks the tests of at least:

 Catalyst-Plugin-Authentication-0.10023
 t/live_app_remote1.t

This commit restores the lines removed, going back to the state of the
last production release, 5.90065:

 git checkout 5.90065 -- lib/Catalyst/Engine.pm

Also re-applied change in 08680694151