print_escaped_cdata only escapes first cdata

[davidmatson]

This works:

BOOST_AUTO_TEST_CASE(one_embedded_cdata_section)
{
    BOOST_REQUIRE_MESSAGE(false, "<![CDATA[EmbeddedCDATA]]>AdditionalTextAfterwards");
}

This produces invalid XML data using -o XML:

BOOST_AUTO_TEST_CASE(two_embedded_cdata_sections)
{
    BOOST_REQUIRE_MESSAGE(false, "<![CDATA[EmbeddedCDATA1]]><![CDATA[EmbeddedCDATA2]]>AdditionalTextAfterwards");
}

I believe the if test here:
if( pos == const_string::npos )

needs to be a loop instead.