[Groff] new .box and .boxa requests

[Werner LEMBERG]

Dear friends,


I've now committed the .box and .boxa requests which behave similarly
to .di and .da but omitting a partially filled line (which is restored
after ending the diversion):

  abc
  .box xxx
  def
  .br
  ghi
  .box
  jkl

will produce

  abc jkl

and `xxx' will contain

  def

-- `ghi' is discarded since the partially filled line before starting
the diversion is restored.


    Werner