set $Strassen::Util::cacheprefix for osm data

... so there's no cache clash when loading different osm data into the
perl/tk app.

Geography/FromMeta.pm

@@ -1,10 +1,9 @@
 # -*- perl -*-
 
 #
-# $Id: FromMeta.pm,v 1.7 2009/06/27 15:34:38 eserte Exp $
 # Author: Slaven Rezic
 #
-# Copyright (C) 2009 Slaven Rezic. All rights reserved.
+# Copyright (C) 2009,2019 Slaven Rezic. All rights reserved.
 # This package is free software; you can redistribute it and/or
 # modify it under the same terms as Perl itself.
 #
@@ -60,6 +59,7 @@ sub center {
 sub center_name { shift->{center_name} }
 
 sub bbox { shift->{bbox} }
+sub bbox_wgs84 { shift->{bbox_wgs84} }
 sub skip_features { %{ shift->{skip_features} || {} } }
 sub skip_feature {
     my($self, $feature) = @_;

bbbike

@@ -809,6 +809,10 @@ if ($city_obj->can("skip_features")) {
 if ($city_obj->is_osm_source) {
     $sBAB_two_track_width = 9999; # effectively turning off
 }
+if ($city_obj->is_osm_source) {
+    my $cacheprefix = ($city_obj->center_name || 'osm') . "_" . join("_", @{ $city_obj->bbox_wgs84 });
+    $Strassen::Util::cacheprefix = $cacheprefix;
+}
 
 # define_item_attribs should be called after determining the $city 
 define_item_attribs();