Permit symbols to be superseded when new symbol files have

    Permit symbols to be superseded when new symbol files have
        been read in, particularly for VxWorks.

        * symfile.c (symbol_file_add):  Use filtered printing and wrap it.
        If we have wiped out any old symbol tables, clean up at end of
        symbol reading.
        (symbol_file_command):  Don't reference symfile_fns if it's zero.