Clean up alter_config() a *lot*. Should now support unlimited line lengths.

Note that it still assumes that teach arctype uses one line only.  It will only add
the specified node to one line, but every time it comes across a line with
the old type, it will replace it with a new line containing every node which uses
the old type.  This is likely not what you want, so only use a single USEPACKER
line per archiver type is you're modifying this by hand.

I'm looking at you access_d.  Your welcome.