Code model: Fix Windows issues (duplicate matches).

Ensure the code model receives file names with clean paths ('/')
and fix paths in the relevant places of the code model. Pass on clean
paths from Cpp reference find and display them correctly in the search
window tooltip.

Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>

src/plugins/cpptools/cppmodelmanager.cpp

@@ -532,7 +532,7 @@ void CppPreprocessor::sourceNeeded(QString &fileName, IncludeType type,
         return;
 
     QString contents = tryIncludeFile(fileName, type);
-
+    fileName = QDir::cleanPath(fileName);
     if (m_currentDoc) {
         m_currentDoc->addIncludeFile(fileName, line);