Make record_store_test_harness work with WiredTiger

This commit adds the appropriate SCons target and shim class to connect
record_store_test_harness to WiredTiger, and fixes the harness to no
longer pass NULL for the OperationContext.
Merge pull request #8 from visemet/dpercy/wt-recordstore-test

Make record_store_test_harness work with WiredTiger