Testing change detection

Detecting if OSM data has changed has a few tricks and quirks.

- Firstly, the data is not always complete (with missing fields), so we can't always compare all the fields.
- Secondly, there are plenty high precision floating point values and even the smallest rounding error can cause false positives.
- Thirdly, processing all the timestamps needs to be done in UTC.
- And of course we don't want to replace more recent data with its older version (when we know the OSM data primitive version.)

All these and more details had to be taken into consideration and tested. There were related bug fixes up till revision 70, which seems to detect changes correctly now.

If you built a database with a previous version of OSM2PostGIS, a lot of changes will be detected because of these bug fixes. Now that the rounding errors and time zone handling are fixed, the database should remain much more stable in future.