testsqlite3: a test for sqlite3gen

This verifies the 'memberdef' table against the generated XMLs.
It accomplishes this by executing a sql query, constructed by iterating
through the children and attributes of the memberdef XML element.

The information translated from xml to sql, is then removed from the DOM,
and the unprocessed bits are printed as warning messages.

usage:
    testing/testsqlite3.py -d /.../doxygen_sqlite3.db -x /.../xml/test__x11_8cpp.xml

output:
WARNING: 'location' has unprocessed attr 'bodyend'
WARNING: 'memberdef' has unprocessed child elem 'briefdescription'
WARNING: 'memberdef' has unprocessed child elem 'detaileddescription'
WARNING: 'memberdef' has unprocessed child elem 'inbodydescription'
WARNING: 'memberdef' has unprocessed child elem 'location'
WARNING: 'memberdef' has unprocessed attr 'kind'
WARNING: 'memberdef' has unprocessed attr 'prot'
WARNING: 'memberdef' has unprocessed attr 'static'
WARNING: 'memberdef' has unprocessed attr 'id'