This work was supported by grants: EET2002 05157 CO5 (to G.V., J.B., A.P.) from MCYT (Spain), CTQ2004 08077 CO2 (to J.B.) and BIO2007 67904 (to A.P.) from MEC (Spain), IB05 136 (to J.B.) from CEC Principado de Asturias, 2005SGR00883 (to A.P.) from Generalitat de Catalunya, DR06/0009 (to N.B.C.) from red Heracles ISCIII (Spain). Funding from Fundação Ciência e Tecnologia (FCT) (Portugal) through POCTI and POCI programmes (Programa Operacional Ciência e Inovação 2010) (to M.J.S.) and FEDER (Project POCI/SAU-MMO/57321/ 2004 to M.R.A.). POCTI/SAU NEU/58735/2004 (to A.M.D.), PTDC/SAU NEU/69123/2006 (to A.M.D.) and FEDER funds (to A.M.D.) are acknowledged. Diffraction data were collected at ESRF beam line ID14 1.