Backport SinonJS bugfix for broken splice() in IE8 and es5-shim

SinonJS 1.9.1 made use of a rare feature in Array#splice that is
implemented in most browsers but not actually part of the ES5 spec.

And in IE8 and es5-shimmed environments, the method was 'broken'
and thus always yielded an empty array causing none of the XHRs
to be responded to.

We can't upgrade to SinonJS 1.10 right now due to
https://github.com/cjohansen/Sinon.JS/issues/506.

Patch source:
 https://github.com/cjohansen/Sinon.JS/commit/60ab124d21

Change-Id: I8882198b1609cb78f16a8269d40bb19df2df127a