Unlock the playlist while waiting for input to finish so that input can freely use signal on the playlist whatever the context is (Closes:#937)

* Possible (not probable) fix for 934. Can't fix as building vlc on win32 is almost impossible

* For the time being, hide simple open. Better three clicks than confusing 
  things :)

The idea is that a given error should be reported only once to the user.
At the moment, for example, we can get:
- "no suitable access module" (printed by module_Need)
 - "unable to create access" (printed by input/access)
 - "unable to open stream" (printed by input/input)
 - ...

The facilities provided here are:
* msg_StackSet( code, message ) : "throw" a new error
* msg_StackAdd( message ) : Append a message allowing to trace the message
* msg_StackMsg() : Retrieve the message

So, in the previous example, module_Need would msg_StackSet( code, "no
suitable access module"), then input/input would add "unable to create
access" and finally, input/input can print the "unable to open stream:
unable to create access: no suitable module" message.

The three functions are context-free, you don't need a vlc_object, so
that we can add verbose error reporting everywhere.

                                   ^^^^^^^^
                   As far as I checked (sed guru required).

code
qt4/components/extended_panels.cpp: Improved some dagerous string
parsing code. This whole function looks very ad hoc to me at the
moment and should be rewritten in a more robust way. In particular
this function will misbehave if a video filter exists whose name is a
substring of another video filter. This change here just makes it less
likely to crash...

Audio track and channel support for JavaScript API. The ActiveX vlc.audio.channel interface still has a bug left.

* gui behaviour change: the textfields are no longer disabled if another protocol is enabled through the knobs. the user can click the fields now to switch the protocol. I'm unsure whether this could and should be done in the disc tab as well. closes #914

* hide the fspanel if VLC looses its front app state in fullscreen mode (by using the app switcher, etc.)