parse the scale attribute of the mesh element if it exists

For example, the crazyflie/crazyflie.urdf uses the scale attribute.
Handling for scale must already exist in the matlab parser but wasn't
working in the cpp parser.  This adds support by introducing a scale
member variable to DrakeShapes::Mesh.

drake/systems/plants/RigidBodyManipulatorURDF.cpp

@@ -350,8 +350,15 @@ bool parseGeometry(TiXmlElement* node, const map<string,string>& package_map, co
     }
     string filename(attr);
     string resolved_filename = resolveFilename(filename, package_map, root_dir);
-    element.setGeometry(DrakeShapes::Mesh(filename, resolved_filename));
+    DrakeShapes::Mesh mesh(filename, resolved_filename);
 
+    attr = shape_node->Attribute("scale");
+    if (attr) {
+      stringstream s(attr);
+      s >> mesh.scale;
+    }
+
+    element.setGeometry(mesh);
   } else {
     cerr << "Warning: geometry element has an unknown type and will be ignored." << endl;
   }

drake/systems/plants/shapes/Geometry.cpp

@@ -153,11 +153,11 @@ namespace DrakeShapes
   }
 
   Mesh::Mesh(const string& filename)
-    : Geometry(MESH), filename(filename)
+    : Geometry(MESH), scale(1.0), filename(filename)
   {}
 
   Mesh::Mesh(const string& filename, const string& resolved_filename)
-    : Geometry(MESH), filename(filename), resolved_filename(resolved_filename)
+    : Geometry(MESH), scale(1.0), filename(filename), resolved_filename(resolved_filename)
   {}
 
   bool Mesh::extractMeshVertices(Matrix3Xd& vertex_coordinates) const 

drake/systems/plants/shapes/Geometry.h

@@ -103,6 +103,7 @@ namespace DrakeShapes
       virtual void getPoints(Eigen::Matrix3Xd &points) const;
       virtual void getBoundingBoxPoints(Eigen::Matrix3Xd &points) const;
 
+      double scale;
       std::string filename;
       std::string resolved_filename;
       bool extractMeshVertices(Eigen::Matrix3Xd& vertex_coordinates) const;