Fix request aborting and schema-relative urls

[homm]

First about aborting. This is unexplainably magic. I can only suppose what IE require closure in this place. But this is fact: requests with onprogress = $.noop fails in many cases (long request, long response, slow connection).

Schema-relative urls required because «Requests must be targeted to the same scheme as the hosting page» is one of XDomainRequest limitation. As I can see schema-relative urls works fine in this place.

[jaubourg]

It would be awesome to have at least a test page that can, even randomly, demonstrate the magic in IE is defeated.

As for the scheme-relative URL, not sure I buy the solution here. First, you have many other schemes than /^https?:/. Second, since it's a limit of the implementation, I'd rather have the transport control the scheme and fail the ajax request if the schemes are different.

And, yes, I'm very late to the party but I swear I didn't see this PR before Oo