SERVER-14168 Don't logOp drop of "inc" collection in MR

The creation and inserts into it are not logOp'd so logging the drop lead to
a warning being printed on secondaries.
SERVER-15111 Treat corruption of final journal section as an expected event

This was always the intention of the code, as a crash may happen while
writing the latest journal section. The code wasn't adjusted when we started
preallocating and reusing journal files and when we started compressing
journal sections, so it ended up treating many common types of corruption as
errors.
SERVER-15087 check for dropped collection in MR
SERVER-15087 Get owned copy of document in MR final reduce