CppLocalRenaming was connected to the initial QPlainTextEdit::document()
and not the "updated" QTextDocument set by
BaseTextEditorWidgetPrivate::setupDocumentSignals().

Broken by

    commit c655d7e5
    CppEditor: Convert to new construction scheme

Change-Id: I2e785a9d62a3bd39d9e613776cfc8e35dd9ff5d4
Reviewed-by: Christian Stenger <christian.stenger@digia.com>