Bump release version to 2.1.3 on develop branch.
Experimental change: move the WT_PAGE.{parent,ref_hint} fields into the
WT_REF structure.
Merge branch 'new-split' into new-split-move-parent-reference

Conflicts:
	src/btree/bt_slvg.c
Merge branch 'new-split' into new-split-move-parent-reference
revert an unnecessary whitespace change
revert an unnecessary change
Fix a comment.
Fix the empty-slot test, the eviction list is WT_REFs, now.
Fix the linkage of the new, in-memory page to the WT_REF structure.
Merge branch 'new-split' into new-split-move-parent-reference

Conflicts:
	src/btree/bt_discard.c
Bug when deepening the tree in a split, didn't connect the newly created
internal child pages to the parent.

Bug when deepening the tree in a split, wasn't fixing up the right set
of WT_REF structures.

WT_REF.home needs to be volatile, we can't cache it in a register
otherwise we might not see the updates when a page splits.

Generalize the function to initialize a root WT_REF, call it from the
3 places that do that (salvage, root-page reconciliation, tree-open).

Simplify the code to look up the WT_REF slot.
Merge branch 'new-split' into new-split-move-parent-reference
Merge branch 'new-split' into new-split-move-parent-reference
Merge pull request #935 from wiredtiger/new-split-move-parent-reference

Move WT_PAGE.parent, WT_PAGE.ref_hint into WT_REF structure.