assert_match as suggested in pull #317

RUBY-676
write_concern from opts for Collection#batch_write_incremental

RUBY-676
refactor rescue OperationFailure out of batch_message_send

RUBY-676
refactor legacy insert return out of batch_write_incremental

RUBY-676
refactor BulkWriteError out of batch_write_incremental into BulkWriteCollection#execute

RUBY-676
refactor "raise" out of batch_write_incremental

RUBY-676
refactor benefit - remove superfluous code

RUBY-676
MULTIPLE_ERRORS_OCCURRED constant from MongoDB Core Server

RUBY-676
Merge branch '1.x-stable-ruby-676' of github.com:gjmurakami-10gen/mongo-ruby-driver into gjmurakami-10gen-1.x-stable-ruby-676