acme, sam: handle >1GB files correctly

TBR=rsc
https://codereview.appspot.com/74060043

src/cmd/sam/sam.h

@@ -113,7 +113,7 @@ enum
 
 struct Block
 {
-	uint		addr;	/* disk address in bytes */
+	vlong		addr;	/* disk address in bytes */
 	union {
 		uint	n;	/* number of used runes in block */
 		Block	*next;	/* pointer to next in free list */
@@ -123,7 +123,7 @@ struct Block
 struct Disk
 {
 	int		fd;
-	uint		addr;	/* length of temp file */
+	vlong		addr;	/* length of temp file */
 	Block		*free[Maxblock/Blockincr+1];
 };