QmlJS: Fix semantic and non-semantic QML error reporting.

The QML snapshot only ever contains valid Documents; to compile a list
of parser problems we need to get at the invalid documents.

To do that, the model manager now provides a Snapshot with up to date,
but potentially invalid documents. That should also be useful for other
things.

Change-Id: I67892f63771c221bf2fe2c2bf0240a0f4e523227
Reviewed-on: http://codereview.qt.nokia.com/3012
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@nokia.com>

src/libs/qmljs/qmljsmodelmanagerinterface.h

@@ -119,7 +119,7 @@ public:
     static ModelManagerInterface *instance();
 
     virtual WorkingCopy workingCopy() const = 0;
-    virtual QmlJS::Snapshot snapshot() const = 0;
+    virtual QmlJS::Snapshot snapshot(bool preferValid = true) const = 0;
 
     virtual void updateSourceFiles(const QStringList &files,
                                    bool emitDocumentOnDiskChanged) = 0;