re-enable scheduler_tests 'manythreads' test case
re-enable scheduler_tests 'manythreads' test case

it passes quite reliably on my system, but we should gather more feedback
about its possible failure to decide how to amend this test

[this is a merge from MVF-BU commit 093e081d9c02f5ea86cc46a3f892434867895fd1]
BTCfork/hardfork_prototype_1_mvf-core,BTCfork/hardfork_prototype_1_mvf-core,BTCfork/hardfork_prototype_1_mvf-core,BTCfork/hardfork_prototype_1_mvf-core,BTCfork/hardfork_prototype_1_mvf-core,BTCfork/hardfork_prototype_1_mvf-core