There are following problems with Access-Control-Expose-Headers.
* If headers in X-Container-Meta-Access-Control-Expose-Headers are
configured, the headers are kept with case-sensitive string.
Then a CORS request comes, the headers are merged into
Access-Control-Expose-Headers as case-sensitive string even if
there is a same header which is not case-sensitive string.
* Access-Control-Expose-Headers is handled by a list.
If X-Container/Object-Meta-XXX is configured in container/object
and X-Container-Meta-Access-Control-Expose-Headers, same header
is listed in Access-Control-Expose-Headers.
This patch provides a fix for the problems.
Change-Id: Ifc1c14eb3833ec6a851631cfc23008648463bd81
d0a026fcb8