[scponly] Feature Request: select allowed external commands at runtime

[Илья Евсеев]

   Hi, folks!
Currently, the set of external commands (unison, sftp, rsync, ...)
is strictly assigned at build time.

IMHO, it should be nice to allow user to modify this list
at run-time using configuration file.

For example, FTP-daemon uses /etc/shells and does not need
to be recompiled when we add /usr/bin/scponly here :-)

The same idea can be applied to setup_chroot:
pass names of binaries to be chroot'ed via command line.

WBR, Ilya