ssl_gnutls: Fix some uninitialized memory warnings
Default twitter's show_old_mentions to 0
twitter: Add support for The United States of America

Land of the Free, Home of the Brave
Makefile: Use wildcard for headers to avoid missing files

The following headers were missing:

dcc.h otr.h lib/base64.h lib/oauth2.h lib/oauth.h lib/xmltree.h
Prevent some "Source ID ## was not found..." warnings

These appear in glib 2.40, and, well, are pretty much useless. But
people complain about them anyway.

Probably fixes trac ticket 1151, at least partially.
Add -lgcrypt when building with OTR built-in

Needed when building without gnutls (which already depends on gcrypt)
RIP native win32 support (use cygwin instead)

It has been broken for a very long time and nobody cared about it.