Reword a comment for clarity.
Allocate the underlying WT_ROW, WT_COL and WT_REF page structures
as part of the WT_PAGE allocation, hopefully resulting in fewer
(and larger) memory allocations when pages enter/leave the cache.
Create a cached list of WT_EXT structures in order to avoid so many
allocation calls.
We're not necessarily holding the live system's spin lock when we
discard extent lists, don't involve the cached WT_EXT list.
If __wt_block_extlist_free() doesn't access the live system's cached
WT_EXT lists, it doesn't need a WT_BLOCK argument, clean all that up.
Merge branch 'develop' into less-allocation

Conflicts:
	src/btree/bt_page.c
Merge pull request #480 from wiredtiger/less-allocation

Reduce the number of times we allocate memory.