Bug 856322 Private Browsing changes for browser feed preview r=Neil.

Also: Remove useless prmem.h include.
Bug 834498 - Remove usage of setPageTitle and isVisited from SeaMonkey's tests, r=Neil

--HG--
rename : suite/modules/test/browser_sanitizer.js => suite/modules/test/unit/test_browser_sanitizer.js
Bug 856872 - Remove obsolete XPCNativeWrapper.unwrap from test_feed_discovery.html, r=Neil