Make method MgSelectionBase::GenerateFilters to be a published Api

[zhanga]

There is a publish Api MgSelectionBase::GenerateFilter(MgLayerBase* layer, CREFSTRING className) in class MgSelectBase, which generates a Fdo filter text for the selections of the specified layer and class. If the key of the layer has more than one column e.g. K1 and K2, the generated filter text is like '(K1=xxx AND K2=xxx) OR (K1=xxx AND K2=xxx) OR ...'. This kind of fitler text cannot be broken into small pieces by MgSelectCommand. If the selection set is very big, it is possible that the generated filter text exceed the max length of Sql statement.
So now we make the method MgSelectionBase::GenerateFilters(MgLayerBase* layer, CREFSTRING className, INT32 selectionSize) to be a published Api. The caller (php, asp from web-tier side) can use this method to get several smaller filter text of a selection to avoid the filter text exceed the length limit.