Mill's exception handler should compare the token version before enqueuing it.

[renjiezh]

Describe the bug
When millbase is handling the exception raised from processing computation token, it should get the latest token and compare the token versions between current one and the latest one.
If versions mismatch, it should ignore the exception and regard it as transient error, unless the number of attempts has reach the limit.

Steps to reproduce
n/a

Component(s) affected
Duchy

Version
0.5.12

Environment
n/a

Additional context