Forward-port [a643d7e59b8fa7b8525dd12ae733baa2a1333f26]

Needed for input_SendEventVout()

It's reserved by gettext. gettext("") will output the headers.

Closes #2300

Untested
Closes #2306

Closes #2308

Closes #2307

Closes #2305

A new variable intf-event has been added.
It supercedes the following variables (they are still present for the
time being):
 - intf-change
 - intf-change-vout
 - rate-change
 - stats-change
and allows to have a better knowledge of the change done.

It is documented in vlc_input.h (in progress).

It allows to avoid the inclusion of input_internal.h

It fixes a bunch of missing locks and remove unused functions.
It splits input_internal.h

It will allows proper locking of p_item.

It will allows proper locking of p_item.

There is no functionnal changes except a few missing events added.

It is a common pratice to allows it for at least TS over RTP.
I have added an error message when using a odd port.

It was preventing mouse to work properly.
Signed-off-by: Christophe Mutricy <xtophe@videolan.org>

Don't forget the break; in a switch !

I seem to have missed these, sorry guys for breaking the build.

The input core does separate playing states for forward or backward direction from the playing state PLAYING_S. If one wants to know in what direction VLC is playing, then he needs to look at the sign value of the "rate" value. Backward playing direction has a negative "rate" value. Forward playing direction has a positive one.