CurlDownloadStrategy: move no insecure redirect check to _fetch
CurlDownloadStrategy: move no insecure redirect check to _fetch

This mainly fixes the problems for subclasses of CurlDownloadStrategy.
More specifically it fixes two things:
 * It allows the no insecure redirect check to be applied to
   CurlApacheMirrorDownloadStrategy.
 * It fixes previous broken CurlPostDownloadStrategy.

Closes #280.

Signed-off-by: Xu Cheng <9a05244150b861e40c78843b801eed71bca54eac@me.com>

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