MFC: r264565
    
    Do not set M_BESTFIT if a strategy has already been provided.  This
    fixes problems when using M_FIRSTFIT.
    
    MFC: r280805
    
    Add four new DDB commands to display vmem(9) statistics.
    
    In particular, such DDB commands were added:
            show vmem <addr>
            show all vmem
            show vmemdump <addr>
            show all vmemdump
    
    As possible usage, that allows to see KVA usage and fragmentation.
    
    Approved by:	re (gjb)