infloop in nntp-retrieve-headers-with-xover in 0.4

infloop in nntp-retrieve-headers-with-xover in 0.4

[Sudish Joseph]

You can lose articles in 0.4 if nntp-retrieve-headers-with-xover ever
sends more than one XOVER (due to nntp-nov-gap).  You'll also infloop.

nntp-send-command now erases the buffer which
nntp-retrieve-headers-with-xover is accumulating it's o/p in.  If
nntp-nov-gap comes into play (depends on what you've got ticked, or if
you have a very small gap) the results of earlier xovers for the same
group are obliterated.  

As a consequence, the code that checks to see if the results of all
the XOVER's sent have arrived will infloop.  Removing the infloop
means you won't see the headers for some articles.  Removing the
erase-buffer will generate a very large *nntpd* buffer after a few
groups.  A real fix requires time I don't have tonight. :-)

-Sudish