Support PKGPATH with "make package-name"

Now dependencies can be listed either by package name, or path to the
package (eg with "make PACKAGE_NAME_TYPE=path build-depends-list").
Users of PACKAGE_NAME_TYPE=html could use a combination of
PACKAGE_NAME_TYPE=name and PACKAGE_NAME_TYPE=path instead now.

No objection from tech-pkg@

(khorben)