HTTP_HOST mangling causes Login to fail for some users #2444

In some environments, a fixup is applied to HTTP_HOST such that it doesn't match the host in SCRIPT_URI. Example:

• open browser to http://example.com/piwik
  $_SERVER['HTTP_HOST'] contains 'www.example.com'
  $_SERVER['REQUEST_URI'] contains 'http://example.com/piwik'

This causes isLocalUrl() and ultimately, the Nonce verification on the Referer to fail.

(In [4750]) fixes #2444

(In [4754]) refs #2444 - relax isLocalReferer() test so that it's comparable to the Origin: test

(In [4756]) refs #2444

(In [4757]) refs #2444

(In [4758]) refs #2444

(In [4760]) refs #2444 - re-enable unit test