grep manpage and usage patch

[Geoff Richards]

The patch attached adds documentation of -z (--null-data) to the
man page (it was already documented in the texinfo, so I copied that),
and also adds it to the usage message.

This patch is against the CVS HEAD just now.

   Geoff

-- 

--- Geoff Richards -------------><-------------- http://ungwe.org/ ---
"I tried to fling my shadow at the moon,
 The while my blood leapt with a wordless song."  --  Theodore Roethke

null-data.patch
Description: Text document