Make ~/.duress directory a toggleable feature.

[nuvious]

Some admins may not trust their users to create duress scripts and want full control to only have the ones in /etc/duress.d run when duress password is used. Modify the module such that it reads in a configuration file /etc/duress.conf to see if the administrator wants to enable ~/.duress for users and create a group that controls which users have their ~/.duress files parsed during login.

[Artoria2e5]

Looks like the pam.conf module arguments are simply passed into the pam_sm_* functions as argc and argv, starting with argv[0] as the first string -- or at least that seems to be how the builtin pam_access understands it.