Start vtkGeoJSONMapFeature class to bring GeoJSON features to vtkMap

Requires including vtkDataSetReaders, which is at:
  https://github.com/OpenGeoscience/vtkDataSetReaders
Also note that vtkGeoJSONFeature class already used in vtkDataSetReaders
First GeoJSON test case - polygon spanning central New York
Add test cases for GeoJSON MultiLineString and Point features
Add vtkMap::FindLayer() method.

Also fix error in ny-points.geojson test file.
Also update readme file to indicate the vtkDataSetReaders requirement.
Merge branch 'master' into john/geojson-feature

Resolved conflicts in:
	Testing/CMakeLists.txt
Merge pull request #56 from OpenGeoscience/john/geojson-feature

John/geojson feature
Use an unambiguous pow call.
make sure computeZoomLevel always returns a value.
Result of comparison against a string literal is undefined.
Remove unneeded statement that causes unused warning.
Add in exporting of classes from vtkMap.
No need to export Teardrop it is only used internally.
Add install rules so we install the library and headers.
Setup fpic rules and osx install name rules.
Properly install the export header for vtkmap.
Require CMake 2.8.11 or above.
Link to curl in a cross platform manner.