Progress on fixing page leaks.
Got things to a compiling (but not linking) in-progress state in preparation for making page_cache_t fully implemented.
Make current_page_t and current_page_acq_t seem mostly complete in this WIP.
Made page_t somewhat loadable, but some tweaks will be needed for make_copy in this WIP.
Seemingly implemented non-flushing aspects of page cache.
Made use of page_ptr_t.
Added explicit keyword to some constructors in page.hpp.
Made page_t::remove_snapshotter potentially delete the pagee.
Renamed some methods in page.hpp.
Made ~intrusive_list_node_t non-virtual and protected.
Made intrusive_list_node_t constructor be protected.
Merge branch 'next' into sam_97_alt
In intrusive_list_t, removed all the validate calls, and made assertions about external usage become guarantees.
Made the block token get reset when the page gets modified.
Removed orthogonal RSI comment.
Basic page txn scaffold.
Merge branch 'next' into sam_97_alt
Merge branch 'sam_97_alt' of github.com:rethinkdb/rethinkdb into sam_97_alt
Made segmented_vector_t be templated on ELEMENTS_PER_SEGMENT (the way it once was).
Make page_txn_t keep snapshotted dirtied pages.