API errors should be JSON

The API was returning Rails (HTML) errors for certain error
conditions, which is inconvenient because it makes it difficult
for the client to extract the error message.

This patch changes add_correspondence to return JSON errors
(still with suitable HTTP status codes) for two common exceptional
conditions, and adds tests.

Conflicts:

	spec/controllers/api_controller_spec.rb

0 files changed, 0 insertions, 0 deletions