x11: set window titles as UTF-8
Always set the X11 window title properties as UTF-8. This is a bit tricky
for X11 window properties which are not specified to use UTF-8, such as
WM_NAME.
We also properly set WM_ICON_NAME, which means the window caption and the
text used in the task bar (of the WM has one) will be the same on most
window managers. Before this commit, WM_ICON_NAME was always hardcoded to
"MPlayer", even if --title or --use-filename-title was used.
Also update the window title only on reconfigure, like it is done in
mplayer-svn commit 34380.