gccxml_plugin has now been tested to work with GCC-4.8 and PyGccXml.

Specific modifications:-

* xml.c
  Revert xml_print_attribute_* changes. The generated XML contained
invalid XML, where '<Attribute>' nodes were misplaced. This might also
bring an XML incompatibility between old GCC-XML output and output from
gccxml_plugin.
  Deleted a few commented out sections.

* gccxml_plugin
  Python's argparse module has some differences compared with a GCC
compiler driver, when it comes to command line options. I've tried to
accomodate for unknown options, that cc1plus would recognise, but it is
quite fiddly, especially when it comes to providing an existing file
that you don't want to be parsed as a source file, e.g. `-include`. In
this case, pass the option without any spaces. e.g.
  `gccxml_plugin -include/path/to/header.hpp

* gccxml_plugin.*
  Delete commented code. May have been something else in .c file.

* CMakeLists.txt
  Add a new compile definition, so that the XML 'revision=' attribute can
be parsed correctly, by pygccxml.