Allow admin created orders to accept payments

(courtesy of @bbuchalter)

Fixes [#3098]
Downcase s3_protocol configuration option to prevent bugs like https://gist.github.com/radar/5793814

As seen in: https://groups.google.com/group/spree-user/browse_thread/thread/152ceac667a80147
Remove check for overview link in homepage_spec
only show payment source form if source required

Fixes #3195
Merge remote-tracking branch 'github/1-3-stable' into 1-3-stable