qdoc: Non-unique section titles produce undetected link errors in the Contents box

Issue
In "Getting Started Programming with Qt Widgets" (http://doc-snapshot.qt-project.org/qt5-release/qtdoc/gettingstartedqt.html), there are multiple subsections entitled "Learn More"

Every instance of "Learn More" in the Contents box links to the first occurrence in the page body instead of the intended occurrence. No warning is generated when building the documentation.

Suggested solutions

1. Make qdoc support non-unique section titles, when nested under different parent sections
2. Make qdoc detect and warn about non-unique section titles, and re-label all sections with unique titles

Personally, I think that it is valid to have multiple "Learn More" subsections in this page, but I can also imagine that supporting this would require rewriting parts of qdoc and may not be worth it.