Added the -G option to allow logins only for users that are members of a certain group. This allows finer control of an instance on who can and cannot login over a certain instance (e.g. password and not key). Needs double-checking and ensuring it meets platform requirements.

*~
*.o
*.a
*.da
*.bb
*.bbg
*.prof
/autom4te.cache
/config.log
/config.status
/dbclient
/dropbear
/dropbearconvert
/dropbearkey
/dropbearmulti
/scp
/scp-progress
Makefile
config.h
config.h.in
configure