This is mainly a refactoring that is useful for an upcoming PR
regarding CORS (smaller patches are better...)
Note that this also fixes a small typo where an extra space was
added when calling {HTTP_HEADER}.put_allow
Initial support for the Cross-Origin Resource Sharing specification.
This allows JavaScript to make requests across domain boundaries.
Also reviewed the filter example to get rid of the context and
the generic classes (we can actually use {WSF_REQUEST}.execution_variable
and {WSF_REQUEST}.set_execution_variable).
Links:
* How to enable server-side: http://enable-cors.org/server.html
* Specification: http://www.w3.org/TR/cors/
* Github: http://developer.github.com/v3/#cross-origin-resource-sharing
