Import of LukeM's ftpd taken from the NetBSD CVS repo on 31-Aug-2006.

Import of LukeM's ftpd taken from the NetBSD CVS repo on 31-Aug-2006.
+ Add PAM and LOGIN_CAP support. Mostly from FreeBSD.
+ Implement option "-D", for running ftpd in standalone mode (daemon).
+ NLST should return 450 instead of 550 upon error, per RFC 959.
+ Add recvbufsize configuration option
+ Remove unreachable code (res could never be NULL here), Coverity CID 712.
+ Set file to NULL after calling fclose(), Coverity CID 2669.
+ Make sure that "su" is initialized before dereferencing it, Coverity CID 1075.
+ Cleanup utmp and utmpx support.