disabling private-browsing tests
Merge pull request #727 from erikvold/pb-tests-disable

Disabling private-browsing tests r=@Mossop
Fix for bug 826406 - Updating widget.contentURL breaks communication between content script and main; r=@erikvold
Bug 808066 - Google custom search button doesn't look like a button; r=@erikvold
Bug 831517 - Force a GC earlier in the test to make sure the test passes. r=gozala
Merge branch 'master' of git://github.com/mozilla/addon-sdk into 777823v2

Conflicts:
	test/test-private-browsing.js