BUMP 2.6.0-rc0
post 2.6.0-rc0
SERVER-12804:smoke.py small_oplog improvements
SERVER-10026 remove most remaining QUERY_MIGRATION tags
SERVER-12826 count10.js test improvements
SERVER-12822 added a multiversion test to verify oplog entries and multivesion compatibility of new updates
SERVER-12804 Revert smoke.py log message change causing test failure