websrv_lib: improve sending of internal error
websrv_lib: improve sending of internal error

gisce/openobject-server,splbio/openobject-server,ovnicraft/openerp-server,MarkusTeufelberger/openobject-server,ovnicraft/openerp-server,splbio/openobject-server,splbio/openobject-server,gisce/openobject-server,MarkusTeufelberger/openobject-server,vnc-biz/openerp-server,gisce/openobject-server,MarkusTeufelberger/openobject-server,vnc-biz/openerp-server