Code review comment for lp:~pbeaman/akiban-persistit/fix_1018526_temp_trees_in_journal

Modified the protocol yet again. Tree handles are now assigned on non-temporary trees as soon as the tree object is created. This permits the Exchange#fetchFromValueInternal to enqueue pages with MVVs before any transaction modifies the tree. (Otherwise the conditional on handle != 0 is required in that code path.) Since this behavior is more similar to what we currently have in trunk, it seemed preferable to restore it.