ExtractArchive rule: Allow the directory to have a grist
Update ICU packages

We extract both packages to the same directory now, since the icu_devel
package depends on the base package and contains relative symlinks to
the libraries. ATM that isn't really relevant, since we link directly
against the libraries from the base package, but we might want to
change that eventually.
BPackageInfo::Parser: Fix error output

The "=" operator isn't actually allowed in a resolvable expression. It
has to be "==" instead.