Peter M. Groen / libmodbus

This time the change is definitive :)

- the return value is used to pass the message length
- remove the hack on exception check in modbus receive
- update tests

- adjusts various comments on return values
- updated tests
- added entry to MIGRATION

- MAJOR changes to the API (see MIGRATION)
- New unit tests
- Removed TODO list
- Updated NEWS & MIGRATION files

This change improves the conformance with the PDU and ADU definitions of the
Modbus protocol and reduces the number of additions.

- 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

- 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

- The coil and registers are wrote by the master and not assigned by the
  slave anymore
- The data used to write are the ones in unit-test.h
- The read test is done after the write test

- Reduce the max message length to 256 (PI_M300)
- s/size/length/

- use uint8_t* for the query

- Major changes to unit-test-master/slave to add 4 tests
- Use new functions to manipulate bits
- Reduce memory usage (allocate only the required space and use
  uint[8|16]_t pointers)

- Separate unit-test-master and test-master-random