add comments regarding strange compiler warnings

gridder_cxx.h

@@ -615,6 +615,8 @@ class GridderConfig
           if (i2>=nu) i2-=nu;
           size_t j2 = nv-ny_dirty/2+j;
           if (j2>=nv) j2-=nv;
+          // FIXME: for some reason g++ warns about double-to-float conversion
+          // here, even though there is an explicit cast...
           dirty(i,j) = tmav(i2,j2)*T(cfu[i]*cfv[j]);
           }
       }
@@ -652,6 +654,8 @@ class GridderConfig
           if (i2>=nu) i2-=nu;
           size_t j2 = nv-ny_dirty/2+j;
           if (j2>=nv) j2-=nv;
+          // FIXME: for some reason g++ warns about double-to-float conversion
+          // here, even though there is an explicit cast...
           grid(i2,j2) = dirty(i,j)*T(cfu[i]*cfv[j]);
           }
       }