openvt: fix gross mismatch between us and "standard" openvt.

openvt: fix gross mismatch between us and "standard" openvt.
  standard one even has different syntax!
  std: "openvt -c 12", we: "openvt 12"
  std: "openvt top", we: complain that "top" is not a number.
openvt: implement -c -w -s (-l -f -v are also accepted but ingnored)

openvt_main                                          188     343    +155
vfork_child                                            -      67     +67
not_vt_fd                                              -      23     +23
packed_usage                                       23932   23952     +20
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(add/remove: 2/0 grow/shrink: 2/0 up/down: 265/0)             Total: 265 bytes
   text    data     bss     dec     hex filename
 801344     641    7380  809365   c5995 busybox_old
 801617     641    7380  809638   c5aa6 busybox_unstripped