Smooth over some cross-browser CSP differences.

* Adding "foo.com" to your CSP via browser-policy now adds both
  "http://foo.com" and "https://foo.com". This smooths over the fact
  that some browsers interpret "foo.com" as "http://foo.com" and some
  interpret it as http AND https.
* Trim trailing slashes from origins. Firefox does not allow content
  from foo.com if you add "foo.com/" to your CSP.
Add frame-src to browser-policy-content.
Use regex to replace trailing slashes from browser-policy URLs.

Thanks glasser!
Merge branch 'bp-improvements' into devel