Long-standing stability bugs fixed in 9pserve.

Update win to use acme interface directly instead of via pipes.
Add comment to pipe about lack of message boundaries.

src/lib9/pipe.c

@@ -3,6 +3,7 @@
 #include <libc.h>
 #include <sys/socket.h>
 
+/* BUG: would like to preserve delimiters on systems that can */
 int
 p9pipe(int fd[2])
 {