Updated Assimp defines to be more flexible

This commit is a follow-up to 85b2019767

Why was export.h removed from assimp < 3.0.0?

collada_urdf/src/collada_to_urdf.cpp

@@ -5,8 +5,7 @@
 #include <collada_parser/collada_parser.h>
 #include <urdf_parser/urdf_parser.h>
 
-#if IS_ASSIMP3
-// assimp 3 (assimp_devel)
+#if defined(ASSIMP_UNIFIED_HEADER_NAMES)
 #include <assimp/IOSystem.hpp>
 #include <assimp/IOStream.hpp>
 #include <assimp/Importer.hpp>
@@ -14,9 +13,8 @@
 #include <assimp/postprocess.h>
 #include <assimp/scene.h>
 #else
-// assimp 2
 #include <assimp.hpp>
-//#include <assimp/export.hpp>
+#include <assimp/export.hpp>
 #include <aiScene.h>
 #include <aiPostProcess.h>
 #endif
@@ -69,7 +67,6 @@ os << "xyz: " << origin.position.x << " " << origin.position.y << " " << origin.
 
 void assimp_file_export(std::string fname, std::string ofname,
                         std::string mesh_type = "collada") {
-#if IS_ASSIMP3
   if (fname.find("file://") == 0) {
     fname.erase(0, strlen("file://"));
   }
@@ -103,7 +100,6 @@ void assimp_file_export(std::string fname, std::string ofname,
     std::string str( "assimp error" );
     std::cerr << ";; " << str << std::endl;
   }
-#endif
 }
 
 // assimp bounding box calculation
@@ -597,9 +593,7 @@ int main(int argc, char** argv)
     cerr << ";; Adding gazebo description" << endl;
   }
   if (vm.count("use_assimp_export")) {
-#if IS_ASSIMP3
     use_assimp_export = true;
-#endif
     cerr << ";; Use assimp export" << endl;
   }
   if (vm.count("original_inertia_rotation")) {