Fix redirects and unretained metadata property.

Fixes broken redirects:
- 302 should change a POST to a GET, like 303 does
- when changing POST to GET, need to strip all content-related headers and body data.
- need to provide a "flattened" NSURL in the redirected request for iOS 8 and WebViews.

Fixes crash when hostAddress has gone away from metadata. Cut & paste bug.