Fix bug in track display sorting

* Track Display column sorting is not being reset when a new playlist is
  selected so the new set of tracks is having the previous sort order
  applied, causing confusion.
Update language files ready for release 2.1.3
Updates NEWS and Changelog
Avoid getting data from an invalid iter

* Crash occurs when deleting all tracks from ipod. Try and mitigate by
  making the loop safer.

* If the iter_next assigns an invalid reference to iter, then the loop
  still makes another iteration and potentially will crash the application.

* Assign the return value of iter_next to valid to avoid the iteration.

* Only try and remove the row if iter is valid

* Thanks to goetz.waschk at gmail.com for pointing out the bug
Updates NEWS and Changelog
Update version script to 2.1.4
Handle when the current playlist is NULL in track display

Thanks to Jonathan Neuschäfer for the patch
Prevent a crash in coverart display if a track has no artist

Use a placeholder for the artist name, if the track lacks the metadata
value.

Thanks to Jonathan Neuschäfer for the patch
Playlist_display - prevent a double-free

This crash could previously be triggered by dragging a newly
created (and not yet saved) playlist from one local repository
to another.

Thanks to Jonathan Neuschäfer for the patch
Fix tabs
Fix possible crasher

When opening the About dialog for the second time, a variable pointed
to freed memory.

Fixes:
(lt-gtkpod:13277): Gtk-WARNING **: Failed to set text from markup due to error parsing markup: Error on line 1 char 36: Invalid UTF-8 encoded text in name - not valid ' \xc5\xc5	h\xdd\xc3	'

(lt-gtkpod:13277): Pango-WARNING **: Invalid UTF-8 string passed to pango_layout_set_text()
Fix showing tracks of selected artist on 64-bit systems

The handler_id is of type gulong (while signal_id is guint); see
http://developer.gnome.org/gobject/unstable/gobject-Signals.html

Bug reported in http://sourceforge.net/mailarchive/message.php?msg_id=30490385
Revert "Fix showing tracks of selected artist on 64-bit systems"

This reverts commit 3732944d096943125e4a51f753644a00726acc68.
Fix showing tracks of selected artist on 64-bit systems

The return value of gdk_threads_add_idle_full() is guint and is
greater than 0; see
http://developer.gnome.org/gdk/2.22/gdk-Threads.html#gdk-threads-add-idle-full

Bug reported in http://sourceforge.net/mailarchive/message.php?msg_id=30490385