Fix build issues on OS X i386.
Fix warnings in externals.
Add enet.

Nice simple library that can be used as the basis for UDP communication,
which is necessary (a) for STUN and (b) potentially to improve
performance when it competes with other connections.

Todo: Satisfy the license clause about including a copy of the license
with all redistributions, as it is not included with binary
redistributions.  As far as I can tell, Dolphin currently ignores
similar clauses in several source files, which should be fixed, and it
doesn't seem like a good reason not to use a particular project.
Add simple STUN client.
Meanwhile... add a copy of the right-click ISO options to the File menu.

This complies with HIGs and will help if users search for a replacement
for "Start Netplay".
Replace Tools->Start NetPlay with two separate options:

- Tools->Connect to Netplay opens a simple dialog asking for IP:port.
  These are intentionally one field, for easier copy and paste.
  (Also, on OS X, the dialog now displays a proper error sheet if the
  connection failed.)

- Right clicking a game, or going to the File menu, and choosing Host
  Netplay Game opens the netplay window.  This way you don't have to
  use a separate, ugly list to select a game, and it's less clicking.

Also stop sending localized strings as unique identifiers over the wire,
that's just silly.

What's missing:

- A way to set your nickname, coming right up.

- A way to set the hosting port.  UDP hole punching is going to give
  you a random external port anyway, and mostly obviates the need to
  have a predictable one.
In ChunkFile, don't switch on the mode for every byte.

The compiler can't optimize it away because of the potential for
aliasing, so it ends up pretty gross.
Ditto for every element of a POD array.
Make ChunkFile use "vectors" for storage rather than looking for a size ahead of time.

This is so that it can be used for netplay too.  Not that it really
saves much to get rid of 400 lines of SFML code, but it feels a little
silly to have two different mechanisms, and ChunkFile would be more
suitable when more types of data need to be sent over the socket
soon(tm).

Instead of using an actual vector it uses a PWBuffer, which is like a
std::vector<u8> but without initialization of elements to 0, avoiding some
preexisting slowdown.  May as well use that everywhere.
Add Packet class.
Bump Netplay version.
Simplify Netplay locking.
Switch NetPlay from SFML to enet.  operator=s abound, ahoy.
Add the ability to change name from within the main Netplay dialog, since it can't be done elsewhere anymore.
Add STUN support.
Put the entries on the player list on two lines.

This should really be improved, but for the time being, it was
impossible for me to see the ping (on OS X).
Bump the Netplay window size.

The old size was too small to fit the new stuff.
Replace STUN with Traversal{Client,Server}.

The key difference is that the server sends a packet to the client (to
be dropped) before the client tries to send to the server.  This allows
it to work in various situations where pure STUN doesn't.
Fix retry button.
Fix evicting (and change test server)