Add fields for lib9p changes.
 [jmk] --rw-rw-r-- M 25987 glenda sys 4420 Oct 30 01:21 sys/include/9p.h
	/n/sourcesdump/2005/1030/plan9/sys/include/9p.h:122,127 - 
	/n/sourcesdump/2005/1031/plan9/sys/include/9p.h:122,129
	  	Tree *tree;
	  	int nchild;
	  	int allocd;
	+ 	int nxchild;
	+ 	Ref readers;
	  };
	  
	  struct Tree {