Permit symbols to be superseded when new symbol files have

    Permit symbols to be superseded when new symbol files have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.

        * dbxread.c (read_dbx_symtab): Allow N_SOL to cleanly take us back
        to the main file, as well as to include files.  Also, put global
        functions into the global psymtab, to make "i fun" work.
        (end_psymtab):  Free named symtabs and psymtabs for a file, once a
        new psymtab for it has been read.