This will allow tests.pkg-config.defaultPkgConfigPackages to run on
hydra without breaking the tarball job.
Regarding the use of null, I'll quote 473ac96 which does lib.hydraJob.
By allowing null, we allow code to avoid filterAttrs, improving
laziness in real world use cases.
Specifically, this strategy prevents infinite recursion errors,
performance issues and possibly other errors that are unrelated to
the user's code.
It now only checks that each derivation's drvPath attribute evaluates.
Previously it checked everything (via toXML) but that causes
derivations with dubious passthru attribute to fail (see commit
70fee5da11).
Now that we don't need to pass "system" arguments anymore, this thing
is *almost* obsolete. (Except for the need to handle assertion
failures, you could just do "nix-instantiate --eval-only ..." on
release.nix.)
derivation evaluate inside the tryEval. This catches cases such as
aufs2-util, which fails due to an assertion in its dependency aufs2.
* Explicitly blacklist "xbursttools" because it gives some
evaluation error in cross-OpenSSL. No idea why, probably due to
some pass-through attribute.
svn path=/nixpkgs/trunk/; revision=23247
