Rename class so Maven runs its tests

Maven is configured to run tests found in classes ending in Tests.
This meant that the tests in BasicErrorControllerIntegrationTest (note
the missing s) were not being run.

This commit renames the test class so that it's picked up by Maven.
Merge branch '1.1.x' and fix failure caused by XML response

Spring 4.1 has added support for XML HTTP message conversion using
Jackson. This was resulting in the response being sent back as XML
rather than JSON. Jackson's XML support doesn't cope well with lists
when it's being asked to deserialize to a Map [1] which is what the
test was doing.

This commit updates the test to indicate that it only accepts
application/json, thereby ensuring that the response can be correctly
deserialized into a Map.

Fixes gh-1715

[1] https://github.com/FasterXML/jackson-dataformat-xml/issues/122