Duplicate key errmsg now varies by server version

also cleanup before test_copy_database

up to date with 2013-12-26

RUBY-676
bulk API writeConcernError raises exception

RUBY-676
ErrorCode module at higher (top) level

also works with nightly 2013-12-30

RUBY-676
BSON serializing error should be marked with INVALID_BSON

RUBY-676
use_write_command? moved to MongoClient

RUBY-676
use_write_command? based on primary for replica sets

RUBY-676