JAVA-1140: Removed erroneous comments about duplicate key errors
JAVA-1140: Added extra assumption to test
JAVA-1128: Don't apply key checking for inserts into system.indexes.  Ensure that key checking and _id creation occurs for all insert paths
JAVA-1134: Added BulkWriteResult.isModifiedCountAvailable(), which returns false if the server is unable to provide the count.  BulkWriteResult.getModifiedCount() now throws if the count is unavailable.
JAVA-1134: Fixed some errant Javadoc