Retry interrupted system calls

[nzjrs]

For Python < 3.5 (https://www.python.org/dev/peps/pep-0475/) it would be good if the library retried system calls on EINTR

This happens frequently with cheap (non-FTDI in my experience) USB-Serial dongles.

[vsergeev]

This is an important catch, thanks. I'll look into it.

[vsergeev]

Marking this issue as help wanted, as I haven't yet encountered the hardware to reproduce and implement this.

[vsergeev]

Closing due to inactivity. Will re-open if this issue resurfaces.