Fix encoding issues related to Python 3 upgrade.

Python 3 str() is a unicode already, so can't be decoded.
subprocess.Popen needs to be in text mode (universal_newlines is the
oldest compatible kwarg for this) in order to do line-based buffering.
In general, all the filesystem encoding stuff we were doing is done by
Python itself now.

zenmap/zenmapCore/NmapParser.py

@@ -1034,7 +1034,7 @@ class NmapParserSAX(ParserBasics, ContentHandler):
     def write_xml_to_file(self, filename):
         """Write the XML representation of this scan to the file whose name is
         given."""
-        fd = open(filename, "wb")
+        fd = open(filename, "w")
         self.write_xml(fd)
         fd.close()