Made page_loader_t be abstract.
Made OVERRIDE and FINAL be lowercase.
Made page_loader_t hierarchy use final attribute.
Moved buffer_cache/alt/ -> buffer_cache/.
Removed unused private field.
Merge branch 'next' into sam_3185_common
Merge branch 'sam_3185_common' into next
Merge branch 'next' of github.com:rethinkdb/rethinkdb into next