Ports/libtiff: Name port as folder name and fix workdir
Previously when installing libtiff as a dependency for another port
it would not find the entry in `packages.db` as the ports that
depend on libtiff would use the folder name rather than the port
name in the dependency list. They did this because there was is a
bug in `.port_include.sh` that cds to the port name and not the
folder the port lives in. This is a workaround for that issue.
EWouters