3781: Set CORS headers in API responses.
3781: Add tests for CORS headers. Turn off CORS headers at OPTIONS /login etc.
3781: Set CORS headers in keepproxy responses.
3781: Add POST method for writing without knowing MD5.
3781: Add allowed headers. Respond to OPTIONS at any path.
3781: Fix error propagation.
3781: Merge branch 'master' into 3781-browser-friendly-servers
3781: Fix OPTIONS routing.
Merge branch '3781-browser-friendly-servers' refs #3781