Ignore exception raised by pip_system_certs not found

[escape0707]

Close #3113

This dependency usually doesn't benefit Linux distros with requests library configured to use system certificate already. And is not packaged by most distros. Making it optional will make most Linux users' installation much easier.

[escape0707]

Maybe requirements.aqt.in should be changed too, if all Linux distros don't need this dependency? I'm not sure about that, tho.

[dae]

Thank you for the change. I think this is fine, but we should probably print a message to stdout in the exception case - something like "pip_system_certs not installed; custom SSL certs may not work".

Distros probably need to make up their own mind about the .in/.txt files - either patching it out or using their own dependency list.

[escape0707]

we should probably print a message to stdout in the exception case - something like "pip_system_certs not installed; custom SSL certs may not work".

Great advice, I'll change the code to print that asap.

Distros probably need to make up their own mind about the .in/.txt files - either patching it out or using their own dependency list.

I think maybe packagers who actually make packages out of source code building should have greater say than me. So I'll leave the judge to them.

[dae]

Thank you!