action.c: Add ForceUpdate flag to ElementList()

ElementList(Need,<refdes>,<footprint>,<value>[,ForceUpdate])
With a 5th parameter case-insensitively named ForceUpdate, the element is
assumed changed and the footprint is loaded from the current library.

Emits a message to the log window reporting the new refdes, value, and
footprint.

Closes-bug: lp-699568

Signed-off-by: Bert Timmerman <bert.timmerman@xs4all.nl>