Scenario: Oracle delay due to high block time

[StrathCole]

The market module already fails to execute when oracle votes are missing, i.e. there did not happen votes for specific currencies in the past period. But this does not apply if the votes are late due to a high block time (e.g. DoS). A block time of 20 seconds could delay oracle update from 30 seconds to 100 seconds. There should be a safeguard preventing the MM to work if oracle votes are older than 45 seconds