Added signal handlers (and placeholder for SEH handlers)

- based on PR 232 (https://github.com/philsquared/Catch/pull/232 - thanks Lukasz Forynski)
- Writes to reporter, so gets all the usual context, but then exits directly (since the stack cannot be resumed) so no summary
- On Windows does nothing, as yet.

include/reporters/catch_reporter_junit.hpp

@@ -168,6 +168,7 @@ namespace Catch {
                 std::string elementName;
                 switch( result.getResultType() ) {
                     case ResultWas::ThrewException:
+                    case ResultWas::FatalErrorCondition:
                         elementName = "error";
                         break;
                     case ResultWas::ExplicitFailure: