error: exit with the given error number rather than 1

Resolves patch request https://bugs.openfoam.org/view.php?id=2827

src/OpenFOAM/db/error/error.C

@@ -200,7 +200,7 @@ void Foam::error::exit(const int errNo)
         {
             Perr<< endl << *this << endl
                 << "\nFOAM exiting\n" << endl;
-            ::exit(1);
+            ::exit(errNo);
         }
     }
 }