sql: use _rowid_ instead of rowid

This doesn't really solve the problem, but reduces the chance
to have a nameclash with rowid, until we come up with something better
we can't fully support tables with a column name _rowid_ but that should
be very seldom

src/sqlitetypes.h

@@ -72,7 +72,7 @@ typedef QVector< FieldPtr > FieldVector;
 class Table
 {
 public:
-    Table(const QString& name): m_name(name), m_rowidColumn("rowid") {}
+    Table(const QString& name): m_name(name), m_rowidColumn("_rowid_") {}
     virtual ~Table();
 
     void setName(const QString& name) { m_name = name; }