Fix AdvancedPlacement handling

[waltweltonlair]

The LayerDefinition schema supports an AdvancedPlacement element on TextSymbol. This element determines whether labels are positioned using an advanced placement algorithm. In particular, it determines if labels on polylines follow the contour of the polyline.

In prior versions of MapGuide this element has never been persisted, even though the default behavior was to enable the advanced placement algorithm for polyline labels. Going forward we want to start using this element to control whether advanced placement occurs, while at the same time allow legacy maps to draw unchanged.

Old maps are missing the AdvancedPlacement element, and therefore the lack of this element implies the advanced placement option be enabled by default. This was already fixed in changeset 2681. In order to specify that a map not use advanced placement, we will tweak the behavior of the ScaleLimit subelement. If this element is 0.0 or less then advanced placement is off. If greater than 0.0 then advanced placement is on. We must update MdfParser to always save the AdvancedPlacement / ScaleLimit elements.

[waltweltonlair]

Fixed with submission ​https://trac.osgeo.org/mapguide/changeset/2729