DotSpatial.Tools: Honor geometry types

twhitvine[CodePlex]
In Analysis / Clip Raster Layer, I can specify a point layer as a quotPolygon for Clipping.quot I should only be able to select polygon layers here, unless the intention is to use the extent of the points as the polygon for clipping. If the latter
is the case, this should be made more evident in the user interface. Otherwise, I shouldn't be able to see the point layer in the drop down.

Start in Analysis / Clip Raster Layer and inspect how the clipping-layer drop-down determines which geometry types it shows. Confirm whether clipping should accept only polygon layers or use point extents as polygons; done means the UI clearly communicates the intended behavior and prevents or supports point-layer selection accordingly.

Written by the indexing model from the issue text.