[Groff] the is \_ escape sequence

[Werner LEMBERG]

I've just rediscovered that groff defines `\_', which is equivalent to
`\[ul]', the underline character.  Clarke writes the following in the
NEWS file (for version 0.6):

  The `\_' character is now automatically translated to `\(ul' as in
  troff.

Funnily, this is documented neither in Kernighan's troff manual nor in
Gunnar's version of it.  I've fixed this documentation glitch now in
the CVS.


    Werner