[UK] Use database for co-ordinate transformation.

[dracos]

If the application is running on a server with GDAL 1.9 (and maybe 1.8),
its OSGB co-ordinate transformation can be up to a few metres out. As we
use the transformation by the database when saving new coordinates, also
use it when fetching so we can match and display accurate information.

[mhl]

Looks good to me - just a couple of things:

• Do you have a link to a bug report describing the problem where GDAL 1.9 is returning wrong results? It would be helpful to include this in the commit message if so. (e.g. I think GDS are using GDAL 1.10, and that might help them to assess if this affect them.)
• I'd probably add a test which adds a Postcode for somewhere in Great Britain, runs it through as_uk_grid and checks the eastings / northings output is as expected. (And the same for a postcode in Northern Ireland.)

[dracos]

I've added a link to the GDAL trac ticket and tests (the GB one I've validated against other data, the NI one doesn't agree but as GDAL + postgres match I'm going to go with that anyway). I've then fixed some other test thing (order mattered and tests failed on firefly) and a co-ord display issue.