[dpkg] Changed rpath configuration for third stage bootstrap during Debian package generation.

This allows the packages to be used inside a chroot without a /proc filesystem, and is more in line
with debian packaging conventions. Since the first and second stage of the bootstrap still use a
relative rpath, building packages still requires a proper /proc mount.
[dpkg] Corrected whitespaces.
Merge pull request #752 from wvdschel/dpkg-rpath-fix

[dpkg] Changed rpath configuration for third stage bootstrap during Debian package generation.