INTEXT-73 Sending multipart SMS messages through a SMPP provider using sar_msg_ref_num, sar_segment_seqnum and sar_total_segments

Example of a multipart message consisting of 3 parts containing 300 bytes:
SMS 1 User Data: 00 03 A4 03 01 [ 135 bytes of message data ]
SMS 2 User Data: 00 03 A4 03 02 [ 135 bytes of message data ]
SMS 3 User Data: 00 03 A4 03 03 [ 30 bytes of message data ]

See: https://jira.springsource.org/browse/INTEXT-73