Fix uncaught error when parsing rest headers, document Started this work as better docs for rest response format. But I found 406 error response was not being tested. Also there was no error for bad Content-Type. In rest.py fix uncaught exceptions due to invalid Accept or Content-Type headers. If Content-type is valid but not application/json return code 415. Document use of accept header (was only shown in examples) and support for q parameter. Describe using .xml and .json extensions to select return format for testing from browser (where setting accept header is a problem). Document 406 error code return. Document 415 error code return and acceptable content types. Previously only doc was in examples. Set up tests for 406 and 415 error codes.

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<p i18n:translate="">You will shortly receive an email
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visit the link indicated in the email.
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