Catch close exception

This closes issue #74 which is that an oracle exception in closeConnection() crashes the process when called by the destructor.

This fix might possibly create a memory leak if the exception is caught and ignored in Javascript, since the resources allocated to the `m_connection` are left in an unknown state.  I did not see any evidence of a leak when using valgrind, but I'm not very experienced with that tool, either.  In any case, as raymondfeng in #74 points out, a leak caused by an exception in terminateConnection() would be an OCCI bug.