filter to search forward or backward in the list of displayed frames for
a matching frame.
When filtering the display, readjust the display to show the "current"
frame if it passed the display filter. When a file is read in, the
first frame becomes the "current" frame; when a frame is selected, it
becomes the "current" frame, and remains so *even if you unselect it*,
until another frame is selected.
Select the first frame when a file is read in.
Disable most of the "Display" and "Tools" menu items if there's no
current capture file, and enable the relevant ones if there is.
svn path=/trunk/; revision=982
Guy Harris