Add io/xml_writer.[ch]pp to build system.

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@7176 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/Makefile.am

@@ -144,6 +144,8 @@ supertuxkart_SOURCES = \
  io/file_manager.hpp \
  io/xml_node.cpp \
  io/xml_node.hpp \
+ io/xml_writer.cpp \
+ io/xml_writer.hpp \
  items/attachment.cpp \
  items/attachment.hpp \
  items/attachment_manager.cpp \