Consolidate adjacent padrange ops

Consolidate adjacent padrange ops

In something like

    my ($a,$b);
    my ($c,$d);

when converting $c,$d into a padrange op, check first whether we're
immediately preceded by a similar padrange (and nextstate) op,
and if so re-use the existing padrange op (by increasing the count).
Also, skip the first nextstate and only use the second nextstate.

So

    pushmark;
    padsv[$a]; padsv[$b]; list;
    nextstate 1;
    pushmark;
    padsv[$c]; padsv[$c]; list;
    nextstate 2;

becomes

    padrange[$a,$b]
    nextstate 1;
    pushmark;
    padsv[$c]; padsv[$c]; list;
    nextstate 2;

which then becomes

    padrange[$a,$b,$c,$d];
    nextstate 2;