Some nitpicky securemessage cleanups

Remove redundant parenthesis and use a consistent commenting style.

Some redundant parenthesis are retained to avoid this pep8 silliness:

  https://github.com/jcrocholl/pep8/issues/126

i.e. to avoid E125 we have the choice of:

        if (md['source'] != source or
                md['destination'] != target or
                md['expiration'] < time.time()):
            raise InvalidEncryptedTicket(md['source'], md['destination'])

or:

        if ((md['source'] != source or
             md['destination'] != target or
             md['expiration'] < time.time())):
            raise InvalidEncryptedTicket(md['source'], md['destination'])

the latter is my preference.

Change-Id: Ic890bfc787a17fc77821e01e586806d1b558d530
Merge "Some nitpicky securemessage cleanups"