Freestyle: lazy load 'export_svg'

Loading XML module, registering etree namespaces... etc
on startup for everyone on chance someone may want to export
an SVG from Freestyle is unacceptable.

This shouldn't have got through the review.

also disable loading when built without freestyle.

release/scripts/startup/freestyle_builtins.py

@@ -20,15 +20,39 @@
 
 import bpy
 
-from export_svg import svg_export_header, svg_export_animation
+if bpy.app.build_options.freestyle:
+    from bpy.app.handlers import persistent
 
-def register():
-    bpy.app.handlers.render_init.append(svg_export_header)
-    bpy.app.handlers.render_complete.append(svg_export_animation)
+    @persistent
+    def freestyle_render_init(scene):
+        render = scene.render
+        if render.use_freestyle:
+            if render.use_svg_export:
+                from export_svg import svg_export_header
+                svg_export_header(scene)
 
-def unregister():
-    bpy.app.handlers.render_init.remove(svg_export_header)
-    bpy.app.handlers.render_complete.remove(svg_export_animation)
+    @persistent
+    def freestyle_render_complete(scene):
+        render = scene.render
+        if render.use_freestyle:
+            if render.use_svg_export and render.svg_mode == 'ANIMATION':
+                from export_svg import svg_export_animation
+                svg_export_animation(scene)
+
+    def register():
+        bpy.app.handlers.render_init.append(freestyle_render_init)
+        bpy.app.handlers.render_complete.append(freestyle_render_complete)
+
+    def unregister():
+        bpy.app.handlers.render_init.remove(freestyle_render_init)
+        bpy.app.handlers.render_complete.remove(freestyle_render_complete)
+
+else:
+    def register():
+        pass
+
+    def unregister():
+        pass
 
 if __name__ == '__main__':
     register()