title: Qt QSqlQuery bindValue works with ? but not with :placeholders
body: <p>I'm working with SQLite, doing insert into table. Folowwing</p>
  
  <pre><code>QSqlQuery testQuery(QString("INSERT INTO test(testcol) VALUES(?)"));
  testQuery.bindValue(0, someQStringObg);
  testQuery.exec();
  </code></pre>
  
  <p>works, but</p>
  
  <pre><code>QSqlQuery testQuery(QString("INSERT INTO test(testcol) VALUES(:val)"));
  testQuery.bindValue(":val", someQStringObg);
  testQuery.exec();
  </code></pre>
  
  <p>don't. testQuery.lastError().text() returns <strong>No query Unable to fetch row</strong></p>
  
  <p>Have no clue why things are that way, but really want to find out.</p>