Recent versions of GTK+ have added a "gtk-label-select-on-focus"

Recent versions of GTK+ have added a "gtk-label-select-on-focus"
property, which selects the entire contents of a label when it comes
into focus.  This property annoyingly defaults to TRUE, which meant that
the labels in simple dialogs and the about box would unexpectedly show
up selected.

Work around this by setting the focus on the "OK" button in the about
dialog and the first button specified in simple dialogs.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@20507 f5534014-38df-0310-8fa8-9805f1628bb7