Peter M. Groen / libmodbus

The function name was confusing because the write operation is performed
before the read. Take care to swap the arguments in the migration process.

Avoid incompatibility with GPLv2 program. This change has been approved by
Tobias Doerffel, Florian octo Forster and Hannu Vuolasaho.

All related scripts and config files have been updated too.

Split the original modbus_receive function in two functions to avoid
the strange -1 value to ignore the sockfd argument.

Reported by Patsy Kaye.
Removed useless asignment at the same time.

Page 38 in the document Modbus_Application_Protocol_V1_1b.pdf:
6.17 23 (0x17) Read/Write Multiple registers

This function code performs a combination of one read operation
and one write operation in a single MODBUS transaction. The write
operation is performed before the read.

The unit test has been updated.

Original patch by Jason Oster

Win32 uses a specific function to close socket.
Reported by Petr Parýzek.

Reported by Antti Manninen and according to Page6 in the document
"MODBUS Messaging on TCP/IP Implementation Guide V1.0b",
------------------------
Unit Identifier – This field is used for intra-system routing purpose.
It is typically used to communicate to a MODBUS+ or a MODBUS serial
line slave through a gateway between an Ethernet TCP-IP network and
a MODBUS serial line. This field is set by the MODBUS Client in the
request and must be returned with the same value in the response by
the server.
------------------------

The cycle will end on a 3.0 release instead of 2.2 as intended.
There are too many changes in the API to keep the same major number.

- return only useful data client side
- available in TCP when a gateway to RTU is used
- need to add isolated handling of indication/confirmation messages

A new API will be committed to remove the slave in TCP communication.

Original patch by Sisyph (eric-paul).

Page 23 of Modbus_Messaging_Implementation_Guide_V1_0b

Inspired by the Clutter project and work done by Florian Forster.

It occurs on first occurence of slave timeout (found with Valgrind 3.3.0).
Reported by Henrik Munktell.

Reported by Henrik Munktell.

Reported and tested by Yishin Li.

Real fix #333455 - IPTOS_LOWDELAY not supported on cygwin
Thank to Yishin Li for the better problem description.