.gitignore: Add MYMETA.yml

We already ignore META.yml, and see
http://www.dagolden.com/index.php/479/mymeta-yml-in-the-wild/
Add more people to AUTHORS

From a suggestion of Anders:

> Actually, since it’s probably best to keep them in an order that doesn’t
> change over time, here are the authors sorted by when their first commit
> was merged:

$ git log origin/master --pretty='%an' --topo-order --reverse | awk '{if (!h[$0]) {print $0; h[$0]=1}}'

I removed duplicates and most of the middle initials.
Fix spelling errors in AUTHORS (caught by ispell)
Update and make configurable the default format

- Rather than http://zephyr.1ts.org/wiki/df, use http://mit.edu/df, which is
  shorter
- Rather than a bare URL, prefix "Config error: see " to make it clearer what
  is going on
- Make the default format configurable using ./configure, to aid users with
  particularly severe length constraints
Add -D_XOPEN_SOURCE_EXTENDED

This is needed for cchar_t on the Travis-CI build machine.
change BarnOwl::Module::Jabber::getServerFromJID to use Net::DNS::RR::SRV methods instead of hash elements (which seem to no longer work).  This unbreaks connecting via jabber to google or facebook