QueryParser: Fix some debug macros
QueryParser: Equation::Match(): Fix generic attribute case

Init size to the buffer size before passing it to
QueryPolicy::NodeGetAttribute(). Since size was 0 by default, we would
only read 0 length data.
packagefs: UnpackingAttributeCookie: Open package

... when reading non-inline attribute data. Generally the package should
already have been opened by the PackageNode owning the attribute (in
InitVFS()), but that isn't the case for queries, which can read
attributes from entirely unsuspecting nodes.

Together with the QueryParser fix that should fix queries involving
non-indexed attributes.