Build process would choke on "unescaped" stuff otherwise,
and these blocks should be blockquotes in the first place.

This is an initial implementation of architecture dependent
contents handling for package lists more or less in the vein
of mkimage-profiles-desktop's one *but* using suffix part to
filter words in or out *not* prefix part to replace it with
a comment marker (thus filtering out lines).

The syntax should be pretty obvious:

  a b@i586 c@x86_64

will get "a b" given ARCH=i586 and "a c" given ARCH=x86_64;
please see doc/archdep.txt for a more elaborate description
and a conversion script.