DBG_PRINTEXCEPTION_C shouldn't be fatal on windows

[3b]

Currently DBG_PRINTEXCEPTION_C (#x40010006) just gives the generic "An exception occurred ..." error, and doesn't allow continuing.

That exception is used to send messages to an attached debugger, something like printing to STDERR. Some libraries use it to print status messages during normal operation, so it would be nice if it wasn't an ERROR.

Ideally, there should be some way to see the error message, since a library might use it to print information before signalling a real exception, or the status messages might be interesting.

Attached patch (against 1.2.9.49-2f571fe) WARNs the message, not sure if that is the best way to handle it or not, probably should at least use a specific warning type. Also not sure if just returning NIL from HANDLE-WIN32-EXCEPTION is correct, but it seems to work.

[Stas Boukarev (stassats)]

In b4bf26582ac92e6270ded439e23957822dffc4b1, slightly modified.

[3b (00003b)]

modified patch dropped the "~a" argument to WARN, so it breaks when the message contains #\~ characters (at best changing the message, usually erroring in FORMAT)