[bitset_t] Add test for walk_bitset
[bitset] Don't visit bits in the tail end of the final word if they're beyond the nr bits in the bitset.

Also shift 1ULL in the test.
[bitset] When reopening a bitset some bits could be lost at the far end.

The number of words necessary to store the bits was being miscalculated.
[progress bar] Add an extra newline at the end
[era] era_dump should show bool values as 'true' or 'false' rather than 0 or 1
[era features] Added tests to check that dump/restore is a noop