Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Cast a ptrdiff_t to int before using it as a printf field width.

Change || into && (braino in previous commit). Also append \n to the
error message.

Major cleanup:

- add __unused where appropriate
- PAM_RETURN -> return since OpenPAM already logs the return value.
- make PAM_LOG use openpam_log()
- make PAM_VERBOSE_ERROR use openpam_get_option() and check flags
for PAM_SILENT
- remove dummy functions since OpenPAM handles missing service
functions
- fix various warnings

Sponsored by: DARPA, NAI Labs

Switch to OpenPAM. Bump library version. Modules are now versioned, so
applications linked with Linux-PAM will still work.
Remove pam_get_pass(); OpenPAM has pam_get_authtok().
Remove pam_prompt(); OpenPAM has pam_{,v}{error,info,prompt}().
Remove pam_set_item(3) man page as OpenPAM has its own.

Sponsored by: DARPA, NAI Labs

Add __FBSDID()s to libpam

Add extra logging detail. This needs a more general solution.

Add a routine for providing feedback via the conversation mechanism
(usually to stderr) for user-reportable errors.

Almost completely rewrite the PAM module options processing
routines, and provide a more extended API for doing this.

Provide an API for debug logging.

Audit and clean up the code.