Need --arch= support in apt-ftparchive

Binary package hint: apt

TEST CASE:
The important part of this is that it does not introduce regressions. This is the focus of the test
case. There is no need to verify the "bug" in the old version:

1. install apt-utils from lucid-proposed
2. create "repo" dir and download into that:
   https://launchpad.net/ubuntu/+archive/primary/+files/4g8_1.0-3_amd64.deb
   https://launchpad.net/ubuntu/+archive/primary/+files/4g8_1.0-3_armel.deb
3. ensure you are in the "repo" dir and run "apt-ftparchive packages ."
4. verify that you see two stanzas that start with "Package: 4g8" and that one has
   Architecture: armel and the other Architecture: amd64
5. now run "apt-ftparchive packages . --arch=armel" and verify that there is only a single stanza
   (with armel as the arch)
6. repeat for amd64 (expected one stanza) i386 (empty output)
7. create new repo2 dir and cd into it
8. download https://launchpad.net/ubuntu/+archive/primary/+files/2vcard_0.5-3_all.deb
9. run "apt-ftparchive packages ." and very that 2vcard is in the output
10. run "apt-ftparchive packages . --arch=i386" and verify that 2vcard is in the output
11. repeat 10 with --arch=amd64 and --arch=armel and verify that 2vcard is part of the output
    (its a arch=all package)

In order to better publish the Ubuntu archive, we need lucid support in apt-ftparchive for --arch=.

We are currently testing a patch, and will upload it once it is confirmed to be sufficient for our needs. The change is minor and isolated to apt-ftparchive.

Rather than maintain a separate fork for the infrastructure, we would like to have this appear in an SRU to lucid.

thanks,
lamont