Fix ebn issues in documentation

Summary: See http://ebn.kde.org/sanitizer/reports/kde-4.x/applications/khelpcenter/index.html

Test Plan: meinproc5 index.docbook works

Reviewers: #documentation, yurchor, ltoscano

Reviewed By: #documentation, yurchor, ltoscano

Subscribers: ltoscano, yurchor, kde-doc-english

Tags: #documentation

Differential Revision: https://phabricator.kde.org/D27546