SERVER-7246 rename internal dbclient_rs auth helper
SERVER-7246 legacy user authentication should use primary preferred read pref
SERVER-7246 test fixup for shard failure tests
SERVER-11971 slaveok versioning logic should also apply to read prefs
SERVER-12041 improve retry logic for read preferences without slaveOk set
SERVER-10026 migrate geoNear to new exec via rewrite
SERVER-9183 redirect startup output to /dev/null in redhat init script
SERVER-11998 Fix typo in agg error message
SERVER-11978 Stop defining __builin_functions to bare functions

It no longer shows performance benefit on current compiler.
SERVER-10026 remove test code that relies on dead code