Add a command to fix South Tynedale's GSS code from 2013-10

South Tynedale UTE was given the wrong GSS code in the last Ordnance
Survey boundary line update in November 2013. They corrected this in
the May 2014 edition, but we need to fix up our historical version of
the area in order to be able to import that.
Add a control file for the May 2014 Boundary Line
Add a command to fix invalid geometries in 2014-05 boundary line

Some of the geometries the Ordnance Survey provided were invalid,
having duplicated start and end points. This command fixes them up.