Fix size of preference tree items

* Added some comments
* Set the b_pausable flage and remove the b_fade/b_stop flags from the dvbsubs.
  They are ephemer and if you need these options set, then figure out another way.

* switched the middle arrow buttons from faster/slower to backward/forward to reflect the same functionality as the usual controller window, thus a more consistent GUI. Thanks to the6thReplicant from the forum for the hint.

Add support to the activex, mozilla, firefox, safari plugin for changing audio track and audio output channel (reverse, stereo, left, right, dolby).

 * skins2/src/generic_layout.cpp: Fixed an old memory leak
This is a forwardport of [18282]

* const string fixes 
* make a couple of functions static

- Do not leak result from utf8_readdir (ALWAYS strdup'ed).

* Add some doxygen comments to some of these functions that warn about vlc_closedir_wrapper and LocaleFree

  * utf8_fopen for: galaktos and snapshots
  * vlc_closedir_wrapper for: webintf, mkv, ncurses and gnutls

  - don't compile pngtest, it's not SDK compatible
  - enable sdk on contrib again

 - Only try Real RTSP in case of rtsp:// realrtsp:// or pnm://
 - Don't use fprintf