Test ber encoding of message_id > 128

@mtodd I'm not sure if there was an issue filed for this, but you mentioned there was a BER encoding issue for message ID's greater than 128. I expected this integration test against OpenLDAP to fail, but it does not. I double checked the same Connection is being reused, and that the message ID is incrementing. Was there other factors I missed?
Here we're checking the most significant bit in the first octet to determine if it's set to one. The ASN.1 BER encoding specifies that this bit is used to indicate the sign of the integer, one for negative, and zero for positive. In the event that it is set to one, we "pad" the value by increasing the length one octet so that the most significant bit is now zero.