[9fans] ssh patch

[Richard C Bilson <rcbilson@plg2.math.uwaterloo.ca>]

I've been having some trouble when piping files to unix systems via
ssh.  I was finding that a number of EOT characters (^D) were being
appended to the file.  Investigating, I discovered that ssh.c can send
multiple eof messages at end-of-file.  I don't know enough about the
protocol to know if this behavior should be allowed, but avoiding the
excess messages fixes my problem.

I don't know what the preferred form for patches is -- I was expecting to
use 'diff -c', but that's not happening, so here's a straight diff:

term% diff -n /sys/src/cmd/ssh/ssh.c ssh.c
/sys/src/cmd/ssh/ssh.c:548 a ssh.c:549,550
> 			else
> 				continue;

(this is in function "fromstdin", just after the break after the test
"++eof > 32")

- Richard