Removed SLICE_ALT in operations.cc up to set_superblock_metainfo.
Removed SLICE_ALT in operations.cc up through get_root.
Removed SLICE_ALT in operations.cc up through check_and_handle_split.
Removed SLICE_ALT in operations.cc up through check_and_handle_underfull.
Removed SLICE_ALT in operations.cc up through get_btree_superblock.
Made get_btree_superblock_and_txn pass expected_change_count to the alt_txn_t constructor.
Merge branch 'sam_alt' into sam_alt_nomir