Description: If any string is set to an environment variable USE_VALGRIND,
when running a memory leak checking tool (e.g., valgrind),
it reduces the noise generated by the entry cache and dn cache.

Sample valgrind outputs from the same operations.
1. with USE_VALGRIND
==16525== LEAK SUMMARY:
==16525==    definitely lost: 5,102 bytes in 155 blocks
==16525==    indirectly lost: 24,655 bytes in 950 blocks
==16525==      possibly lost: 13,294 bytes in 433 blocks
==16525==    still reachable: 2,209,801 bytes in 17,937 blocks
==16525==         suppressed: 0 bytes in 0 blocks
==16525== Reachable blocks (those to which a pointer was found) are not shown.
==16525== To see them, rerun with: --leak-check=full --show-reachable=yes

2. no USE_VALGRIND
==25738== LEAK SUMMARY:
==25738==    definitely lost: 5,102 bytes in 155 blocks
==25738==    indirectly lost: 24,655 bytes in 950 blocks
==25738==      possibly lost: 23,862,444 bytes in 863,885 blocks
==25738==    still reachable: 3,093,988 bytes in 41,603 blocks
==25738==         suppressed: 0 bytes in 0 blocks
==25738== Reachable blocks (those to which a pointer was found) are not shown.
==25738== To see them, rerun with: --leak-check=full --show-reachable=yes

Thanks,
--noriko