Working on the workspace sanitizer (ancestor of the workspace emulator)
final rollbacks were needed to unwind allocations. There was however a
branch where error handling was missing a workspace release, and it was
fine before the introduction of the final rollbacks.

To avoid turning the workspace emulator into a DoS vector the rollbacks
are now only enforced for emulator builds. The specific "insufficient
workspace" log is amended to ensure future changes to the session
workspace footprint don't accidentally remove test coverage for that
branch. The same could be done for other "insufficient workspace" logs
in the PROXY protocol parsing.

Refs 0632b846 (req: Prevent early rollback)
Refs ce71896a (sess: Plug conceptual leak)
Refs 246b1eb1 (busyobj: Plug conceptual leak)
Refs 5b4f0f1a (htc: Defer workspace rollbacks for request tasks)
Refs #3644

Spotted by Alf's single process fuzzing setup that we should eventually
revisit.

Refs #3152