Usernames in updates posted to /user should be checked case-insensitively

If an application has lowerCaseOutput set then it will never receive mixed-case names.

When user details posted to the '/user' resource are checked to make sure the payload entity matches the username in the database this is currently a case-sensitive check, which fails because the returned lowercase output doesn't match the mixed case stored in Crowd.

For consistency with Crowd's case-insensitive, case-preserving behaviour this check should also be case-insensitive. The update shouldn't affect the existing case in the database.