Add a wrapper around pySerial to monkey patch support for custom baudrates

[kakaroto]

This is only useful if the pyserial version installed is lower than 2.7 since that doesn't support custom baudrates on linux.

The monkey patch will replace the set_special_baudrates function in the serial module with the version of the function from pyserial 2.7 which allows the use of 250000 baudrates on Linux. If pyserial is 2.7 or newer, it won't do anything.

[eldir]

Wouldn't changing the requirements.txt to pyserial>=2.7 be the way forward here?

[kakaroto]

I hadn't noticed there's a requirements.txt file, but yes, changing the requirements there would be good, but this patch is meant to make printrun work with pyserial 2.6, not change its requirements to 2.7.
The purpose being for it to work on machines that can't simply have pyserial 2.7 installed. More specifically, for debian jessie (current stable debian release) which only has 2.6 in its repositories : https://packages.debian.org/source/jessie/pyserial

[kliment]

The license on this is problematic - Printrun is GPLv3 whereas this is AGPLv3. @kakaroto, if you're the author of this, would you be willing to change the license? Essentially all the code appears to be a straight copy from pyserial anyway.

[kakaroto]

@kliment, thanks for looking into this. I've updated the code with a couple of fixes and changed the license to match the pyserial license.
The first fix is to prevent monkey patching for OSX which is not needed and already works, and the second one, is to make sure the monkey patch doesn't get executed if we're running pyserial > 2.7. While that last one is not necessary, is to safeguard in case things change in the future and a potential pyserial 4.0 doesn't have that TCGETS variable that the monkey patch checks for, which might make it think it needs to patch pyserial.

For your information, pyserial 2.7 was Python Software Foundation License, but pyserial 3.0 is using a 3-clause BSD license. Since the set_special_baudrate (the copied code) was not modified and is essentially identical between pyserial 2.7 and 3.0, I've chosen to use the updated license for that code and have changed the monkey patch code into 3-clause BSD license, which is compatible with the GPL.

Thanks!