SERVER-15541 Don't do anything with MMAPV1Flush unless IsForMMAPV1
SERVER-13951 Changes that depend on rollback
SERVER-13635 Allow KVEngines to opt out of doc-locking
SERVER-1153 Clean up Heap1RecoveryUnit and implement recordChange()
SERVER-1153 Improve RecordStoreHeap

* Now supports rollback
* No more reinterpret_cast<>
* Fixed an iterator invalidation bug in the reverse iterator
SERVER-13635 Have KVCatalog do locking if the storageEngine doesn't support doc locking
SERVER-1153 Heap1 is now using KVEngine
SERVER-13635 Add StorageEngine::isMmapV1()
SERVER-13635 KVStorageEngine metadata rollback