Since we're not using SHA-1, remove this string from the code,
and just change it to "checksum" as a human-readable string.
The XML output was broken when a file was added, because a line with
"new:" was unconditionally output, along with the new file's checksum,
rather than this being part of the XML. So conditionally call the
original report_sumchange() function if we're outputting XML, otherwise
execute the code to print "new:" and the checksum.
Add additional information to the XML version of the missing file
element. Specifically, and in the following order, add:
permissions, type, uid, gid, size, modification_time.
Add an XML Schema Definition file for the integrit XML output.
This allows easy parsing and object manipulation using tools such as
JAXB, and also allows the validity of the output to be checked with,
for example, xmllint --schema integrit.xsd.