sparql_xsd_checkfns - fix order so double and float are correct
Check XSD double format and add tests.

(rasqal_xsd_check_double_format): Validate according to
http://www.w3.org/TR/xmlschema-2/#double which also refers to
#decimal and #integer.

(rasqal_xsd_check_float_format): Use rasqal_xsd_check_double_format()
which is the same.

(main): Add positive and negative tests for
rasqal_xsd_check_double_format