Core: fix unnecessary forward-slash in include path

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8369 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Tests: fix file include paths.

This change is needed as result of the trunk re-organisation caused by
the adoption of Grunt. See #5160

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8370 cdf35c40-ae34-48e0-9cc9-0c9da1808c22