sqlite3-ruby has been deprecated for sqlite3, mysql not required

The choice of database really belongs to the rails app, not this gem...
But sqlite3 makes testing easier.

Signed-off-by: Chris Riddoch <criddoch@globe.gov>
ruby-debug has been superceded by debugger.

Signed-off-by: Chris Riddoch <criddoch@globe.gov>
introduce version_at_column

The version_at_column names a column which will hold a timestamp for a
revision.  While the version_column could itself be replaced with a
timestamp column, the converse isn't true, so both are useful.

Signed-off-by: Chris Riddoch <criddoch@globe.gov>
version_at column shouldn't itself be versioned, added to migration and test fixtures

Signed-off-by: Chris Riddoch <criddoch@globe.gov>
Updated queries to use Arel, fixed lurking bug of a hardcoded column name.

I don't like all the references to original_class, but changing that
would be quite a bit of work...

Signed-off-by: Chris Riddoch <criddoch@globe.gov>
Oops. Whitespace fix.

Signed-off-by: Chris Riddoch <criddoch@globe.gov>
Missed a couple places to define the version_at column in the tests, fixtures, etc.

Signed-off-by: Chris Riddoch <criddoch@globe.gov>
Add the column for version_at created from the migration helper.

Signed-off-by: Chris Riddoch <criddoch@globe.gov>
Actually assign to the version_at_column when a new version is created

...and hesitating a bit with save_version.

Signed-off-by: Chris Riddoch <criddoch@globe.gov>
Documentation fix, changed? was renamed to altered? somewhere.

Signed-off-by: Chris Riddoch <criddoch@globe.gov>
Initially correct; without this line, a new version will have a nil timestamp.

Though, I had the wrong variable for the column name.  Oops.

Signed-off-by: Chris Riddoch <criddoch@globe.gov>