Attr.vala: add an XML example
Make clone_node's return value be an unowned Node; its memory is managed by its GXml.Document whose node_dict it lives in, and we don't want the caller to deal with its referencing
gxml/{Element,Node}.vala: add documentation for memory usage
Node.vala: change doc
test/valgrind/Makefile: to use 'make run', get user to pass name of program to test as a macro
test/valgrind: move a .supp rule to gtype.supp from glib.supp
test/valgrind/gtype.supp: add some proper labels