Allow citadel / libcitadel to be built outside their source directory, e.g.:
drwxr-xr-x - citadel
drwxr-xr-x - contrib
drwxr-xr-x - ctdlphp
drwxr-xr-x - ctdlsalearn
drwxr-xr-x - ctdlsh
drwxr-xr-x - libcitadel
drwxr-xr-x - webcit