PAM_Extern

The password is now passed on stdin instead of an
environment variable to prevent it from showing up
in "ps auxe". Every "malloc" call is now checked
for success. Debug output is now realized with
PAM's D macro instead of fprintf(stderr) and
_pam_overwrite and _pam_drop are used instead of
free().

pam_extern now passes the password as an
environment variable instead of on the command
line. This prevents the password from showing up
in the output of "ps".