Better/Explicit exception handling
WS_Attachment hack to make it work with Suds

Disclaimer: THIS IS A HACK (but it does as intended)
- Made it work by monkey-patching  no-op method `replyfilter` of the
`suds.bindings.binding.Binding` class.
- The monkey-patch version tries to parse the reply string, as Suds would.
- If no SAX-parsing exception is raised, return the string untouched.
- If a `SAXParseException` is raised, detect the payload boundaries using RegEx
  and use those payloads to construct MIME Messages and extract the the payload
  content.
- It's assumed the first payload is the XML response, so this XML is parsed
  (using lxml) and the "return" node's text is replaced with the second
  payload's content.
- The lxml parser is instantiated with every flag available that could
  transform the XML. When called with the default parser, some namespaces and
  prefixes where replaced.
- The resulting XML (after replacing the text of the result node) is serialized
  as a string and then returned.
Fixes invalid NULL byte.
Merge pull request #3 from mobilerider/ws-attachment-hack

WS-Attachment hack