- fix proxy mode when 'redirect_to_exact=True' is set config, don't redirect in proxy mode
- more general prefer support, moved to content_rewriter to support preference<->mod mappings
- add 'banner-only' preference mapped to bn_ modifier
- proxy mode: allow 'raw' and 'banner-only' preferences
- proxy mode: 'Prefer: rewritten' forced to 'banner-only', served with 'Preference-Applied: banner-only'
- tests: test proxy with prefer header, 'redirect_to_exact=True', add 'banner-only' to Prefer header tests in rewriting mode
- support Prefer on top-frame url in framed mode, Prefer check runs before custom response
- update Prefer test fixtures to test framed vs frameless and no-mod vs mp_ modifier, all combinations
- 'enable_prefer: true' in config can be used to enable experimental Memento Prefer behavior
- Prefer header support both redirect and non-redirect style negotiation, extending existing Memento patterns
- Prefer header can be applied both on memento and timegate endpoints
- for redirect style negotiation, Prefer results in a redirect to final memento (if needed), both on Timegate and URL-M (Memento Pattern 2.3)
- for non-redirect style negotiation (Memento Pattern 2.2), Prefer header affects content being served and changes the Content-Location to the canonical representation
- Vary: Prefer and Preference-Applied headers always added to URL-M and Timegate responses
