Fix a few -Wshorten-64-to-32 warnings

Author: Dane Springmeyer

src/mapnik_image.cpp

@@ -145,7 +145,7 @@ std::shared_ptr<image_any> copy(mapnik::image_any const& im, mapnik::image_dtype
     return std::make_shared<image_any>(mapnik::image_copy(im, type, offset, scaling));
 }
 
-unsigned compare(mapnik::image_any const& im1, mapnik::image_any const& im2, double threshold, bool alpha)
+std::size_t compare(mapnik::image_any const& im1, mapnik::image_any const& im2, double threshold, bool alpha)
 {
     return mapnik::compare(im1, im2, threshold, alpha);
 }

src/mapnik_parameters.cpp

@@ -165,7 +165,7 @@ mapnik::parameter get_params_by_index(mapnik::parameters const& p, int index)
     throw boost::python::error_already_set();
 }
 
-unsigned get_params_size(mapnik::parameters const& p)
+std::size_t get_params_size(mapnik::parameters const& p)
 {
     return p.size();
 }

src/python_grid_utils.cpp

@@ -71,13 +71,13 @@ void grid2utf(T const& grid_type,
     // start counting at utf8 codepoint 32, aka space character
     std::uint16_t codepoint = 32;
 
-    unsigned array_size = data.width();
-    for (unsigned y = 0; y < data.height(); ++y)
+    std::size_t array_size = data.width();
+    for (std::size_t y = 0; y < data.height(); ++y)
     {
         std::uint16_t idx = 0;
         const std::unique_ptr<Py_UNICODE[]> line(new Py_UNICODE[array_size]);
         typename T::value_type const* row = data.get_row(y);
-        for (unsigned x = 0; x < data.width(); ++x)
+        for (std::size_t x = 0; x < data.width(); ++x)
         {
             typename T::value_type feature_id = row[x];
             feature_pos = feature_keys.find(feature_id);
@@ -201,14 +201,13 @@ void grid2utf2(T const& grid_type,
     mapnik::grid::data_type target(data.width()/resolution,data.height()/resolution);
     mapnik::scale_grid(target,grid_type.data(),0.0,0.0);
 
-    unsigned array_size = target.width();
-    for (unsigned y = 0; y < target.height(); ++y)
+    std::size_t array_size = target.width();
+    for (std::size_t y = 0; y < target.height(); ++y)
     {
         uint16_t idx = 0;
         const std::unique_ptr<Py_UNICODE[]> line(new Py_UNICODE[array_size]);
         mapnik::grid::value_type * row = target.get_row(y);
-        unsigned x;
-        for (x = 0; x < target.width(); ++x)
+        for (std::size_t x = 0; x < target.width(); ++x)
         {
             feature_pos = feature_keys.find(row[x]);
             if (feature_pos != feature_keys.end())