epubveri for calibre 0.4.2

• Clicking a column heading sorts the panel under every Sort setting, not
  just two of them. Doitsu asked for header sorting (374940 #28) on a panel
  that has had it since 0.3.0 — under Severest first and Least severe
  first it worked, and under Document order nothing happened at all.

  Filling the table switches Qt's sorting off, so the rows are not re-sorted
  once per row as they arrive. QTreeView.setSortingEnabled(False) also
  clears the header's sectionsClickable, which is not in its name: the
  constructor had asked for a clickable header and the first validation
  quietly took it away. The click then never reached the handler that exists
  for exactly this case, so Document order meant unsortable rather than
  unsorted until you click, which is what it was meant to mean.

  The panel still opens in the book's own order under that setting — Qt has
  no unsorted state once sorting is on, so the only honest way to offer it is
  not to sort — and the first click now sorts, the next reverses, as
  everywhere else. No sort arrow appears until the first click, because until
  then nothing is sorted.