Peter M. Groen / libmodbus

This time the change is definitive :)

- upgrade to WAF 1.5.3
- smaller WAF scripts
- fix using of modbus.h with WAF
- updated configure.ac and Makefile.am files
- change include paths in test files

- remove header and checksum length from modbus_param_t
- use new const tables

- new functions modbus_slave_init_listen_tcp, modbus_slave_accept_tcp,
  modbus_slave_slave_receive.
- removed printf in modbus.c: 'Connection closed'
- new slave test, bandwith-slave-many-up
- updated build scripts
- updated MIGRATION document file

- use strerror instead of error number

Thanks to Justin Carroll to have reported and tested my patch.

Invalid error check in modbus_init_listen_tcp

- Add many comments to receive_msg and modbus_receive functions.
- The use of response_length for good response was confusing.

- Return test on read and recv slightly more robust
- Fix a comment

- code is easier to understand
- code is bit faster.

- reduce the number of variables to store return values (status,
  query_ret and response_ret -> ret)
- add some comments

modbus_check_response() crashes on an invalid exception code

The test is now outside of check_crc16 and directly included in
receive_msg().

- s/datas/data/
- the warning is now an error
- add some checks in modbus.c
- add unit tests
- remove the TODO item
- minor 80 columns changes

execution.

MODBUS Messaging on TCP/IP Implementation Guide V1.0b.

The transaction identifier is used to associate the future response
with the request.  So, at a time, on a TCP connection, this identifier
must be unique. There are several manners to use the transaction
identifier:
- For example, it can be used as a simple "TCP sequence number" with a
  counter which is incremented at each request.
- It can also be judiciously used as a smart index or pointer to
  identify a transaction context in order to memorize the current
  remote server and the pending MODBUS request.

It's slower to pass non aligned values.