Collector #2320: HTTPResponse setHeader lowercased keys but getHeader did not, causing lookups of 'Content-Type' to fail

Fix DateIndex date display; unpack stored integers into something meaningful. This fixes Collector #2316.

Repair (and simplify) tests in response to
http://www.zope.org/Collectors/Zope/2308.

Configure subscribers in code, not by loading ZCML.

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Collector #2300: delimit *all* headers with CRLF; accumulated_headers and appendHeader use \n for delimeters and never get corrected on output

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Collector #2298: webdav.Resource.COPY and webdav.Resource.MOVE did
not send the expected copy/move events.

not send the expected copy/move events.

Note: Tests live in OFS.tests.

- Protect various security-setting-mutators with this decorator.

- Add a request method decorator to AccessControl, creating decorators that limit a method to one request method only.
- Protect various security-setting-mutators with a POST-only decorator.

Add a 'method' key to the HTTPRequest.other, containing the uppercased REQUEST_METHOD. This makes HTTPRequest a little bit more compatible with Zope3 IHTTPRequest.

Protect against setNumberOfThreads disappearing after first use.

Use a decorator to save and restore thread-local state.