Update caveats now that mdb_reader_check exists
Less aggressive page_spill

spilling all possible pages is a waste because the majority will be
needed again. Just do 1/8th of the dirty list instead.
Tweak prev commit

If somehow "need" is larger than the list size, don't
try to fake out the dirty list.
Simplify last commits
mdb_page_spill(): Fix nested txn mt_dirty_room
ITS#7670 Tweak cursor_del0

Always leave cursor pointing at "next" node, if any.
Find next sibling if we're already at end of current page.
ITS#7671 always return the key for a dup val
Speedup deletion from spill_pgs
Cleanup prev commit
Another take on spill_pgs and deletes
mdb_page_unspill(): Fix dirty_room in nested txn
ITS#7672 fix mdb_dbi_flags

Use a txn instead of env argument. Only return persistent flags.
Allow mdb_env_set_mapsize() on an open environment

The caller is responsible for making sure no transactions are
active in this process before resizing. This is slightly lighter
weight than doing a full env_close/env_open cycle.
Bump version to 0.9.8
Add a changelog