installer: fix ability to use a custom OpenSslDir when building the Win32 installer.

The actual assignment was missing an "env." prefix.
installer: add the ability to use a custom bzip2 directory in the Win32 installer.

Previously, the bzip2.dll was always taken from the Ice directory.
This is because we previously used ZeroC's binary Ice releases, which
included a bzip2.dll that we could use.
PulseAudio: fix access to protected enums in AudioInput and AudioOutput.

The SampleFormat enums in AudioOutput and AudioInput are meant to be
used in subclasses of AudioOuptut and AudioInput, and because of that,
they're marked protected.

PulseAudioSystem has used these protected enums for some time, without
triggering any warnings. However, recent versions of Clang error out
on this behavior (and rightly so).

To fix this issue, this change modifies PulseAudioSystem to access the
SampleFormat enums via PulseAudioOutput and PulseAudioInput, instead
of going through AudioOutput and AudioInput directly. PulseAudioSystem
is already a friend class of PulseAudioOutput and PulseAudioInput, so
it can access the protected members of AudioOutput of AudioInput just
fine, as long as it happens via PulseAudioOutput and PulseAudioInput.

Originally reported on the Debian BTS (as #753273) by
Alexander <sanek23994@gmail.com>

Reported on the Mumble issue tracker (as #1302) by
Chris Knadle <Chris.Knadle@coredump.us>
Comment memcpy from #1305

Document why memcpy in this location is safe and assert on possible future
implementation mistakes that might leave it to long.
plugins: add magic values for all previously supported ABIs (and a couple of new ones) to mumble_plugin.h.

Add all previous magic values we've used since at least 1.2.0.
(Though I think the MUMBLE_PLUGIN_MAGIC value for MSVS2008 x86
goes back even further!)

This also adds a new magic value for the MSVS2013 x64 ABI, and
a generic default for "unsupported" ABIs.

Unsupported in this context means platforms/ABIs that we aren't
distributing plugins for via the auto-update mechanism. Those
platforms typically only have a single plugin, which is the
"link" plugin distributed with Mumble itself.
plugins: add missing 'elif'; fix indentation of MSVS2008 'if' block.
celt-0.7.0-src, .gitmodules: point the submodule to our own CELT 0.7.0 code base to fix Windows/amd64 build of celt-0.7.0.
Make Mumble and Murmur build on Windows/amd64.
Log IP address on failed login

* Show the IP address of the rejected connection in the mumble-server log.
** Allows use in ban-software which scans logs (requested for fail2ban).
*** Note that the address format will differ with activated IP obfuscation.
* Applied patch from https://sourceforge.net/p/mumble/bugs/861/
which implements the FR #1303 and fixes debian bug 627139 [1]
* This patch was already automatically applied to our Ubuntu PPA builds [2]

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=627139
[2] https://github.com/mumble-voip/mumble-ubuntu-ppa/blob/master/patches/02-reject-with-ip-in-log.diff
Adjust method comment to match usage

* The ice authenticator API was changed to allow returning -3 on auths,
the method comment of Server::authenticate now reflects this change as well.
** See 88d41e10, 6e8c8939
* The surrounding code already checks for the return value -3
(caller of method Server::msgAuthenticate)
Use set the 'os' query parameter to 'WinX64' when doing version checks and plugin updates on Windows/amd64.
OSInfo: use 'WinX64' as the OS identifier for Windows/amd64 builds.

The OS string from OSInfo is used in places such as log files, and
in the Server Info and User Info dialogs.

I think it'll be beneficial in the long run to be able to
distinguish an x86 build from an amd64 on in these places.

Technically, the full OSInfo dump has an is64bit flag, but it's not
visible in the aforementioned places - only the OS string is. The
isb64bit flag is only used when submitting usage stats.
Set mumble_app.dll's version to 1.3.0.
plugins: temporarily disable game plugins on Windows/amd64. the 'link' and 'manual' plugins are still built.
Overlay_win: move early-return on WinX64 below variable initializations.
installer: add x64 platform to the installer.
installer: additional update to the .sln file for x64.
installer: fix whitespace issue in Plugins.wxs.
installer: make WiX produce a working x64 installer.
installer: remove vccorlib120.dll from the installer.