Add an explicit ZOOM:: prefix to the catch(exception& e) clause.

Add an explicit ZOOM:: prefix to the catch(exception& e) clause.
Some systems (e.g. the Debian 3.0R0 that I use at work) choke on this
otherwise, saying that "exception & err" is a syntax error, while others
(e.g. the Red Hat 7.2 that I use at home) seem fine with it.  I guess
that in the former case, the second catch() block is wrongly perceived
as falling outside the scope of the "using namespace ZOOM" directive.