add errorString output argument to IFile::save()

this centralizes error reporting (in fact, in most cases it adds any in
the first place).

Task-number: QTCREATORBUG-1619

src/plugins/cmakeprojectmanager/cmakeproject.cpp

@@ -735,10 +735,11 @@ CMakeFile::CMakeFile(CMakeProject *parent, QString fileName)
 
 }
 
-bool CMakeFile::save(const QString &fileName)
+bool CMakeFile::save(QString *errorString, const QString &fileName)
 {
     // Once we have an texteditor open for this file, we probably do
     // need to implement this, don't we.
+    Q_UNUSED(errorString)
     Q_UNUSED(fileName)
     return false;
 }