Minor whitespace change.
Merge branch 'next' into sam_97_alt

Conflicts:
	src/btree/btree_store.hpp
Merge branch 'next' into sam_97_alt

Conflicts:
	src/btree/secondary_operations.hpp
	src/containers/disk_backed_queue.cc
	src/containers/disk_backed_queue.hpp
	src/rdb_protocol/btree.cc
Fixed some slight conflicts in SLICE_ALT mode after merging from next.
Seemingly got alt cache integrated into all of rdb_protocol/btree.cc.
Got the alt cache integrated into rdb_btree.cc.  Everything except rdb_protocol/protocol.cc.
Merge branch 'next' into sam_97_alt
Implementation of alt cache in rdb_protocol/protocol.cc up to line 1500.
Pushed alt cache integration in rdb_protocol/protocol.cc down to line 1700.
Whoops.  Removed duplicated call in rdb_protocol/protocol.cc.
Got all alt cache stuff compiling, but some stuff does not link.
Removed alt cache linker error in depth_first_traversal.cc.
Fixed alt cache linking problems related to secondary_operations.cc (integrated alt cache code into the whole file).
Made set_superblock_metainfo implementation for alt cache, fixing one linker error.
Made check_and_handle_split implementation support the alt cache.
Got the alt cache integration compiling.
Set SLICE_ALT to 1.
Merge branch 'next' into sam_97_alt
Merge branch 'sam_1714' into sam_97_alt
Made write_durability_t be an enum class.