Finesse TCP timeouts for upstream connections.

Timeouts for TCP connections to non-responive servers are very long.
This in not appropriate for DNS connections.

Set timeouts for connection setup, sending data and recieving data.
The timeouts for connection setup and sending data are set at 5 seconds.
For recieving the reply this is doubled, to take into account the
time for usptream to actually get the answer.

Thanks to Petr Menšík for pointing out this problem, and finding a better
and more portable solution than the one in place heretofore.

src/blockdata.c

@@ -101,7 +101,7 @@ static struct blockdata *blockdata_alloc_real(int fd, char *data, size_t len)
 	      memcpy(block->key, data, blen);
 	      data += blen;
 	    }
-	  else if (!read_write(fd, block->key, blen, 1))
+	  else if (!read_write(fd, block->key, blen, RW_READ))
 	    {
 	      /* failed read free partial chain */
 	      blockdata_free(ret);
@@ -228,7 +228,7 @@ void blockdata_write(struct blockdata *block, size_t len, int fd)
   for (; len > 0 && block; block = block->next)
     {
       size_t blen = len > KEYBLOCK_LEN ? KEYBLOCK_LEN : len;
-      read_write(fd, block->key, blen, 0);
+      read_write(fd, block->key, blen, RW_WRITE);
       len -= blen;
     }
 }