To-Do list of open, but not critical issues.

* player.c: Rewrite thread communication to use message passing
  instead of shared memory.

* player.c: Replace pthreads with glib threads.

* player.c (init_player): There are lots of possible errors, probably
  we should define and set ERRNO on error.

* newtestwin.c: Add confirmation dialog if user is about to create a
  new test while the current test is valid.

* resultwin.c: Implement better-looking result table, use GtkCellView
  or something like.

* Add tooltips.
