With monolingual files, source string can change without changing
checksum, we need to properly detect this and update unit if needed.

See also issue #118

This reverts commit ce1fdc85.

Accepting suggestion now has different entry in changes database.

Currently translated at 57.5% (458 of 797)

Currently translated at 100.0% (797 of 797)

It was not that useful as I hoped for.

While this is faster with smaller amounts of data, it slows down with
huge tables.

Currently translated at 98.6% (786 of 797)

Currently translated at 100.0% (797 of 797)