* data/vaucanson.xsd: Change the structure of the semiring description.
	Semirings with set=`ratSeries' are now `numericalSemiring's and
	recursive. The <semiring> tag is not recursive anymore.
	* doc/xml/xml_proposal.tex: Update accordingly. Fix some errors. Remove
	the first references to the tag <transducer>. Enhance some descriptions.
	* include/vaucanson/xml/tools.hxx: Update accordingly.
	* src/tests/xml/label_node_ref.xml,
	* src/tests/xml/trans_ref.xml,
	* src/tests/xml/geometry_ref.xml,
	* src/tests/xml/r_ref.xml,
	* src/tests/xml/z_ref.xml,
	* src/tests/xml/b_ref.xml,
	* src/tests/xml/fmp_ref.xml,
	* src/tests/xml/session_ref.xml,
	* taf-kit/tests/b_to_transpose.xml,
	* taf-kit/tests/t2_u-compose_u2.xml,
	* taf-kit/tests/b_transposed.xml,
	* taf-kit/tests/inverted_t1.xml,
	* taf-kit/tests/t2.xml,
	* taf-kit/tests/u2.xml,
	* taf-kit/tests/non_ambiguous2.xml,
	* taf-kit/tests/ambiguous.xml,
	* taf-kit/tests/non_ambiguous.xml,
	* taf-kit/tests/t1_compose_u1.xml,
	* data/automata/tdc-rw/quot-3-rw.xml,
	* data/automata/tdc-rw/add1-rw.xml,
	* data/automata/b/a1.xml,
	* data/automata/b/b1.xml,
	* data/automata/b/div3base2.xml,
	* data/automata/b/double-3-1.xml,
	* data/automata/b/ladybird-6.xml,
	* data/automata/z/b1.xml,
	* data/automata/z/c1.xml,
	* data/automata/tdc/t1.xml,
	* data/automata/tdc/u1.xml: Update accordingly.