[HttpFoundation] Docblock for Request::isXmlHttpRequest() now points to Wikipedia
merged branch stloyd/feature/request_phpdoc (PR #6599)

This PR was merged into the 2.0 branch.

Commits
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666283c [HttpFoundation] Docblock for Request::isXmlHttpRequest() now points to Wikipedia

Discussion
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[2.0][HttpFoundation] Docblock for Request::isXmlHttpRequest()

Docblock now points to [Wikipedia entry](http://en.wikipedia.org/wiki/List_of_Ajax_frameworks#JavaScript) instead of pointing all known JS frameworks.

Replacement for #6444.