[sasl] GS2 fixes

[Simon Josefsson <[e-mail]>]

GS2 is in AUTH48 so I took some time to revise my implementation and
noticed that the GSS-API interface descriptions were underspecified.  I
intend to send the following request to the RFC editor unless there are
any objections within a few days.  The text is mostly copy'n'paste from
similar descriptions in RFC 2743/2744.

/Simon

OLD (section 10.1):
      minor_status      Integer, modify
                        Mechanism specific status code.

NEW:
      minor_status      Integer, modify
                        Mechanism specific status code.

      desired_mech      OID, read
                        Identifies the GSS-API mechanism to query.

      sasl_mech_name    buffer, character-string, modify, optional
                        Buffer to receive SASL mechanism name.
                        The application must free storage associated
                        with this name after use with a call to
                        gss_release_buffer().

      mech_name         buffer, character-string, modify, optional
                        Buffer to receive human readable mechanism name.
                        The application must free storage associated
                        with this name after use with a call to
                        gss_release_buffer().

      mech_description  buffer, character-string, modify, optional
                        Buffer to receive description of mechanism.
                        The application must free storage associated
                        with this name after use with a call to
                        gss_release_buffer().

OLD (section 11):
      o  mech_type OBJECT IDENTIFIER -- must be explicit mechanism,
         and not "default" specifier

NEW:
      o  mech_type OBJECT IDENTIFIER -- must be explicit mechanism,
         and not "default" specifier.  Caller should treat as read-only
         and should not attempt to release.

OLD (section 11.1):
      minor_status      Integer, modify
                        Mechanism specific status code.

NEW:
      minor_status      Integer, modify
                        Mechanism specific status code.

      sasl_mech_name    buffer, character-string, read
                        Buffer with SASL mechanism name.

      mech_type         OID, modify, optional
                        Actual mechanism used.  The OID returned via
                        this parameter will be a pointer to static
                        storage that should be treated as read-only;
                        In particular the application should not attempt
                        to free it.  Specify NULL if not required.

OLD (section 11.1):
      GSS_S_BAD_MECH    The desired_mech OID is unsupported

NEW:
      GSS_S_BAD_MECH    There is no GSS-API mechanism known
                        as sasl_mech_name