Pull extract_payload_from_request out of expose_api.
Needs to be used in new version of API decorator and resulted in too much nesting in there the way it was.
Introduce new generation of API decorator...
Add improved error handling. Introduce error code.

Use new decorator with tested methods in histories API.
Add functional tests for pages API.
Touch up pages API in response to test cases. Update pages API to use newer API decorator.
Parse error codes/messages from new JSON file.
Same python interface to this data, but the data can now be reused by clients in other languages (e.g. potentially automating the creation of typed Java exceptions).
Merged in jmchilton/galaxy-central-fork-1 (pull request #294)

New API Decorator