Fix startup

Sometimes TokuDB can't open an existing DB even if it was closed
cleanly, unless the RECOVER option is used.
Fix sequential reads

BDB's lock table would fill up if reading many records in a single TXN.
Use READ_COMMITTED to allow read locks to be released immediately. This
only affects the sequential (forward and reverse) read tests.
Revert "Fix startup"

This reverts commit 6dfb4cfa66185a5b3d867213a4406679e9828d80.
My mistake, TokuDB had crashed due to out-of-memory, was
not a clean exit.
Touch retrieved data, force page access