Test support enhancements:

Test support enhancements:

_xml_failure():  Clean up the output message so the first line doesn't
    wrap in the typical case.

CharData typedef:  If count is less than 0, consider it "unset".  This
    is used in the new support to check attribute values.

accumulate_characters():  Handle storage->count < 0.  Allow XML_Char
    to be more than one byte.

accumulate_attribute():  New function: store the value of the first
    attribute encountered in parsing.  This needs the concept of a
    CharData that is unset to allow capturing a value that is an empty
    string.

check_characters():  Handle storage->count < 0.  Allow XML_Char to be
    more than one byte.

run_character_check():  Create a local parser so that both
    run_character_check() and run_attribute_check() can be used in a
    single test function.

run_attribute_check():  New function: check that the value of the
    first attribute in a document matches the expected value.