Port to udisks2 from fork IGP/pam_usb + minor fixes

[drmfinlay]

Hello. As mentioned here, I think merging from @igp's fork would be good for porting pam_usb to udisks2, as a lot of the issues with @luka-n's PR are fixed. My fork also fixes a code style issue and adds an AUTHORS file. I'm not sure if any other contributors need to be listed there.

[andrey-utkin]

Please see #31 (comment)

[aluzzardi]

@Danesprite @luka-n: I'm confused as to which PR to merge between this and #31

[drmfinlay]

Hello @aluzzardi. Sorry for the late response.

I must admit it has been quite some time since I used pam_usb. From the looks of it, my PR includes some of @igp's changes and a few of the style changes you requested in #31. I assume the issue with xscreensaver mentioned in #31 is still unresolved, but perhaps that could be fixed separately?

Since it's been a while, I'll give this branch a try again and let you know if it still works with libudisks2.

[drmfinlay]

Incidentally, the README links to your pam_usb wiki no longer work. I can update them in this branch if you like.

[drmfinlay]

I can confirm this is still compiling and working properly for me using libudisks2 version 2.8.1-4. I had to move the pam_usb.so file from /lib64/security to /lib/x86_64-linux-gnu/security for it to work though. I guess the path for PAM module files has changed on newer distributions.

[aluzzardi]

Thanks a lot, @Danesprite.

I see there's an open comment by @andrey-utkin -- any concerns in merging this, or good to go?