prime was broken during an experiment and not put back.
retain the Bprint for speed

Reference: /n/atom/patch/applied2013/primefix
Date: Tue Jun 18 21:58:26 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/primes.c	Tue Jun 18 21:58:09 2013
+++ /sys/src/cmd/primes.c	Tue Jun 18 21:58:09 2013
@@ -107,8 +107,8 @@
 			if(pt[i] > limit)
 				exits(0);
 			Bprint(&bout, "%d\n", pt[i]);
-//			if(limit >= big)
-//				exits(0);
+			if(limit >= big)
+				exits(0);
 		}
 		nn = 230;
 	}
@@ -145,8 +145,8 @@
 			if(temp > limit)
 				exits(0);
 			Bprint(&bout, "%.0f\n", temp);
-//			if(limit >= big)
-//				exits(0);
+			if(limit >= big)
+				exits(0);
 		}
 		nn += tsiz8;
 	}