Catch all unexpected errors in with Pyax queries and report as a PyaxUnexpectedError with details.

Use case: at one point, Salesforce returned a non-valid-xml response to a query, which it should never do. Although we couldn't fix it, a good error here indicating what SF returned would have helped in diagnosing and reporting the error to SF.

The traceback showed where there error occurred, but why was the sobject_result a string and what string was it?

Traceback (most recent call last):
  File "/srv/salesforce/production/production/sfi-salesforce/bin/../canonical/salesforce/remote_orders/licences.py", line 213, in <module>
    LicenceKey.refill()
  File "/srv/salesforce/production/production/sfi-salesforce/bin/../canonical/salesforce/remote_orders/licences.py", line 140, in refill
    lic_count_result = sfdc.query(qry)
  File "/srv/salesforce/production/production/sfi-pyax/pyax/connection.py", line 615, in query
    return self.__processQueryResult(query_result)
  File "/srv/salesforce/production/production/sfi-pyax/pyax/connection.py", line 663, in __processQueryResult
    query_result_batch = self.__resultToObject(sobject_records)
  File "/srv/salesforce/production/production/sfi-pyax/pyax/connection.py", line 321, in __resultToObject
    if isinstance(sobject_result.get('Id'), list):
AttributeError: 'unicode' object has no attribute 'get'