SERVER-6157 Remove FastArray

It has no remaining users since the old external sorter was removed. Since it
has no advantages over a std::vector, it should never be used again.
SERVER-15111 Treat corruption of final journal section as an expected event
SERVER-13951 Add a WUOW around logOp in applyOps
SERVER-15192 Temporarily disallow rollback of logOp

Since there are currently logOp listeners that are not rollback safe we are
temporarily disallowing rollback of all operations once they get to the
logOp. This will work since (today) we only call logOp once we know an
operation will succeed and commit.