setup and exceptions

["Robert Collins" <robert dot collins at itdomain dot com dot au>]

Well,
	I've just tried, and exceptions do work. The stdc++ library I've
got here appears to have been built without thread support, so we can't
use cross-thread exceptions. In fact IIRC we can only use exceptions
within a single thread.

This means that some care is needed before we introduce any exception
using code. I'm not sure if gcc needs to be reubuilt if/when threads are
enabled... If the answer is yes, then simply getting a threaded
libstdc++ is not enough.

If the answer is no, and "someone" were to make a prebuilt mingw
libstdc++ available with thread support, then we can use exceptions more
freely.

For the moment, when I get time, I'll review what occurs in each thread,
and what mechanism we might use to safely get some benefits.

i.e. if the only time we have multiple threads is a separate GUI update
thread, then as long as that update thread never creates or absorbs
exceptions, we are safe.

Rob