importer: patches-applied failures are sometimes unsolvable

samba 2:3.6.3-2 fails to `dpkg-source -x` in modern versions of dpkg.

This in turn is basically what our importer algorithm is doing, with `quilt` manually, which also fails. Which means samba's patches-applied branches cannot proceed.

I think it makes sense to add a patches-applied blacklist file of the form:

<srcpkg> <version>

which the importer algorithm would read in like the other files and choose to skip patches-applied import for if present (basically for exactly cases like this one).