Bug#544994: apt-ftparchive: "generate" fails with unclear error message when component is not found

["Yann Dirson" <dirson@debian.org>]

Package: apt-utils
Version:

$ apt-ftparchive -c .../release.conf generate
.../apt-ftparchive-extras.conf -o
BinDirectory::ExtraOverride=.../override.intrepid.extra.extras
 pool/extras:E: Tree walking failed - ftw (2: No such file or directory)
Done Packages, Starting contents.
Done. 0B in 0 archives. Took 0s

strace reports:
16065 stat64("./pool/extras", 0xbff0b8a4) = -1 ENOENT (No such file or
directory)
16065 lstat64("./pool/extras", 0xbff0b8a4) = -1 ENOENT (No such file or
directory)

This tells that one component listed in
APT::FTPArchive::Release::Components was not found in the pool, and the
error message should make that clear.