Peter M. Groen / libmodbus

Thanks to Perry Kundert for bug report and initial patches.

The report slave id function returns the number of bytes as the _return_
value, and does not include it as the first byte in the dest buffer.

Update documentation to reflect reality.  There's no missing
functionality, just slightly confusing documentation.

- add byte timeout tests (TCP backend only)
- update and improve documentation
- long timeout values are now uint32_t so it changes the API
  to disable byte timeout

Thank you AlexMaz.

https://www.securecoding.cert.org/confluence/display/seccode/DCL37-C.+Do+not+declare+or+define+a+reserved+identifier
Not applied to libmodbus constants for now...

POSIX-1.2001 for fd_set. Thanks to spider391Tang.

- update documentation
- 5 new tests
- updated NEWS file
- avoid include of time.h

The index variable shadowed a variable in the standard library causing
warnings. Renaming the 'index' variable to 'idx' resolves the issue.

It's strongly recommended to update your libmodbus library if you
use it in a slave/server application in a not trusted environment.

Debian package of libmodbus 3.0.4 already contains a patch to
mitigate the exploit but the patch isn't as strong than this one.

Related to https://github.com/stephane/libmodbus/issues/83

Thank you very much James Nutaro.

Thanks to Jan Kardell.