SERVER-15979 remove even more mmap_v1isms

Closes #866

Signed-off-by: Benety Goh <benety@mongodb.com>
Fix index multikey settings
SERVER-15950 Optimize handing of writingPtr

* No longer need to allocate memory per call to writingPtr.
* Write intents within a single WUOW are coalesced if overlapping or adjacent.
* Committing a WUOW only grabs the groupCommitMutex once.
SERVER-13635 Test collection and index rollback
SERVER-15998 don't fall-through on WriteConflictExceptions in write command update
SERVER-15179 Run authSchemaUpgrade steps even when in version 28SCRAM
SERVER-16000 store integral values of wired tiger statistics instead of string values
SERVER-7676 make sort memory limit configurable
Change --wiredTigerDatabaseConfig to --wiredTigerEngineConfig
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
Further reduce memory usage of manyclients.js
Finish changing --wiredTigerDatabaseConfig to --wiredTigerEngineConfig
SERVER-16041 cache_size estimation does not work on OSX
Import wiredtiger-wiredtiger-2.4.0-275-gc4f14ea.tar.gz from wiredtiger branch develop
Tune WT default cache_size up to 50% memory
SERVER-16023: abort mongod on WT_PANIC