Dear Maintainer,

pbuilder will generate thousands of "ln: Invalid cross-device link"
errors when the base image and the build place are in two different
devices.

The documentation says that the solution to this problem is to set
`APTCACHEHARDLINK=no` in pbuilderrc.

It would be nice and (very helpful to new users of pbuilder) if pbuilder
automatically detected that it cannot use hardlinks and switched to
`APTCACHEHARDLINK=no`, warning the user about the occurred problem but
going forward in the building process.

Alternatively pbuilder could stop after the first error. There is no
need to spam the console with thousands of errors. After the first error
pbuilder already know that the setup of the chroot will fail.