This directory will replace $BIRCH/admin if BIRCH is 
uninstalled. This directory has dummy source files
(eg. cshrc.source, profile.source) that will
delete lines containing the string #_BIRCH from
.cshrc, .login, .profile, .bash_profile and .bash_login.
These lines would not have a deleterious effect on users'
accounts if left in, but it's cleaner to delete them.
