Add a hack to pkgtools to install to a different root. This differs from

Add a hack to pkgtools to install to a different root.  This differs from
using PREFIX as the installed files don't get relocated, but all the tree
appears in PKG_FAKEROOT, including PKG_DBDIR.

This won't work for all packages and isn't ment to either.  Pkgtools are
evil hackery anyways and this adds even more.  This will be used in
nrelease to support addition of packages by using the host tools and not
the target tools.