v.vol.rst: improve wording of warning (https://trac.osgeo.org/grass/ticket/3100)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@69439 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.vol.rst/main.c

@@ -637,7 +637,7 @@ int main(int argc, char *argv[])
 		}
 	    }
 	} else
-	  G_warning(_("Unable to create cellout raster map without cellinp"));
+	  G_warning(_("Unable to create <%s> raster map without cross_input raster map being specified"), cellout);
 	ertot = 0.;
         
 	out_cond1 = (outz != NULL) || (gradient != NULL) || (aspect1 != NULL)