Make non-bundled apps work with wxmac 3.0.0

Non-bundled apps (e.g. gnuplot) do not show the wx window with wxmac 3.0.0 (or show it after a huge amount of time).

For instance, `gnuplot` (compiled with `--wx`) shows its plot window after several minutes.

The upstream patch included here (see http://trac.wxwidgets.org/ticket/15613) fixes this.