[Bromley] disambiguation for White Horse Hill

This street is on boundary of Bromley with Greenwich, so a simple
disambiguation of $town = "chislehurst" falls foul of UKCouncils->
area_check.

It may be worth overriding area_check in general, but in mean time,
setting a specific postcode (on the Bromley side of the administrative
boundary) allows the map to be seen.
Example 'inverted' KML file for Manila.

Just an example, not to be used as is!
Merge branch 'example-ph-hole' of github.com:mysociety/fixmystreet
Testing example-ph-hole in my cobrand