SERVER-16027 verbose mongos cursor messages for read_pref_multi_mongos_stale_config.js
refresh snapshot in between batch updates; update multikey flag correctly
SERVER-16029 inserts into WT nonunique index should not fail with DUPLICATE_KEY
SERVER-15972 Prevent stepping down without holding the global lock
SERVER-16034 correctly identify CRUD ops in SyncTail::fillWriterVectors
Merge remote-tracking branch 'upstream/master'