Put back BEAST_CATCH_UNHANDLED_EXCEPTIONS macro, but disabled by default

Builds/VisualStudio2012/BeastConfig.h

@@ -74,6 +74,16 @@
 //#define BEAST_COMPILER_CHECKS_SOCKET_OVERRIDES 1
 #endif
 
+/** Config: BEAST_CATCH_UNHANDLED_EXCEPTIONS
+    This will wrap thread entry points with an exception catching block.
+    A customizable hook is provided to get called when unhandled exceptions
+    are thrown.
+    @see ProtectedCall
+*/
+#ifndef   BEAST_CATCH_UNHANDLED_EXCEPTIONS
+//#define BEAST_CATCH_UNHANDLED_EXCEPTIONS 1
+#endif
+
 //------------------------------------------------------------------------------
 //
 // Libraries