Generate NASTRAN USET cards from an imat_ctrace
USET = CTRACE2USET(CTRACE,UNAME,FILENAME)
CTRACE is an imat_ctrace.
UNAME is the name of the uset (8 characters maximum).
FILENAME is an optional input containing the output filename. If it is not supplied, or it contains wildcards (? or *), you will be prompted with a graphical file dialog.
USET is a cell array of strings containing the USET cards.