MX-1290 Only set the memcmp magic for primary key indexes, new or
existing. Add a test that verifies the sort order and uniqueness of an
_id index that is not the primary key.

Conflicts:
	src/mongo/db/collection.cpp
	src/mongo/db/index.cpp
	src/mongo/db/index.h
	src/mongo/db/indexer.cpp
bump debian changelog to 2.0.0-rc.1
Revert "MX-1290 Only set the memcmp magic for primary key indexes, new or"

This reverts commit ae5934bc5b607a1f8a0d54f76731a3d774b634ef.
Merge branch 'bugfixes/tokumx-2.0'

Conflicts:
	debian/changelog