Shape: deal better with shapefile directories with foo.shp and FOO.DBF, particularly for REPACK support, and particularly for Windows OS (on Linux, foo.shp and FOO.DBF will be 2 different layers)

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@25863 f0d54148-0727-0410-94bb-9a71ac55c965