sound support: use gstreamer+pulseaudio to provide efficient sound in/out over network

[Antoine Martin]

What we have there kinda works, but there are many issues that need improving/resolving:

• bandwidth: pulseaudio's TCP protocol is a bandwidth pig... We must ensure we only use it over fast links (need better detection?)

Edit: see original description for the approach that was abandoned (pure pulseaudio)

[Antoine Martin]

Went a completely different route: pulseaudio simply could not be made to not suck up all the bandwidth, so I implemented the sound pipes using ​gstreamer's rtp module:

• initial network stuff: messages to request start/stop sound (both for server and client): r2561
• more network stuff: some tricky code to get right to set the ports to use (set by server if tunneled, by client if not!) and remove pulseaudio from xpra via a patch + command line switch (would conflict with what we do), also remove pulseaudio from win32 build: we no longer need it. r2556
• Use an external process as it appears that gstreamer+twisted+pygtk does not seem to play nice (and in any case, we need the ability to daemonize the process on the server): r2587 and r2585
• Allow users to select the sound devices to use for input and output: r2645
• Win32 needs its own .EXEs (and its own build file and DLLs, and directory...) for the gstreamer RTP code: r2653