[Mailmunge] Fetching all Headers.

[list at ptld.com]

> I'm not sure what problem you're trying to solve.  MIME::Head let's you get
> any header just as pulling it out of a hash would.


End goal is having %headers i can loop and match filters to, without knowing 
the names of what the headers will be.

Basically the simplest form of (pseudo code):
     my %headers = $ctx->mime_entity->head->get_all("*");
     while (my ($key, $value) = each %headers) { ... }

If the IO::File method is the only other way, same same as manipulating the 
$ctx->mime_entity->head->as_string; to me.