Partially reverts eaa4db148d. Used
together with nix-shell it results into unresolvable domains. For
example: `nix-shell -p libxml2` spawns a shell with non-working DNS.
chroot should remove such unpurities.
This allows, for instance, `docbook_xsl' to be visible (as part of
`$XML_CATALOG_FILES') by packages that use it as a build input.
svn path=/nixpkgs/trunk/; revision=11047
xsltproc from downloading DTDs from the network, which is impure.
This caused a lot of problems with Gnome builds in the build farm,
because those downloads are slow and would sometimes fail.
The setup hook also sets up $XML_CATALOG_FILES.
svn path=/nixpkgs/trunk/; revision=9471
