From reading the source I'm pretty sure it doesn't support multiple Yubikeys, hence
those options are useless.
Also, I'm pretty sure nobody actually uses this feature, because enabling it causes
extra utils' checks to fail (even before applying any patches of this branch).
As I don't have the hardware to test this, I'm too lazy to fix the utils, but
I did test that with extra utils checks commented out and Yubikey
enabled the resulting script still passes the syntax check.
c35917e330