Change xml_named_node_iterator to be bidirectional and to match xml_node_iterator in terms of internals

git-svn-id: http://pugixml.googlecode.com/svn/trunk@960 99668b35-9821-0410-8761-19e4c4f06640
Ignore stream errors generated by a failing tellg() for non-seekable streams

git-svn-id: http://pugixml.googlecode.com/svn/trunk@961 99668b35-9821-0410-8761-19e4c4f06640