libmp: mptouv bug fix
 [rsc] --rw-rw-r-- M 80611 glenda sys 723 Mar  5 15:45 sys/src/libmp/port/mptouv.c
	/n/sourcesdump/2006/0305/plan9/sys/src/libmp/port/mptouv.c:43,49 - 
	/n/sourcesdump/2006/0306/plan9/sys/src/libmp/port/mptouv.c:43,49
	  
	  	v = 0ULL;
	  	for(s = 0; s < b->top; s++)
	- 		v |= b->p[s]<<(s*sizeof(mpdigit)*8);
	+ 		v |= (uvlong)b->p[s]<<(s*sizeof(mpdigit)*8);
	  
	  	return v;
	  }