"Export PDUs to File" pops up a dialog, so put "..." after it.

Also, capitalize "File" in the GTK+ version (it's already capitalized in
the Qt version).

Change-Id: I27eb27022930b1c0e0321cd1a1446c3b9dc1bd17
Reviewed-on: https://code.wireshark.org/review/3072
Reviewed-by: Guy Harris <guy@alum.mit.edu>