remote-mediawiki: allow fetching namespaces with spaces

we still want to use spaces as separators in the config, but we should
allow the user to specify namespaces with spaces, so we use underscore
for this.

Reviewed-by: Antoine Beaupré <anarcat@debian.org>
Signed-off-by: Antoine Beaupré <anarcat@debian.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/mw-to-git/git-remote-mediawiki.perl

@@ -65,6 +65,7 @@ chomp(@tracked_categories);
 
 # Just like @tracked_categories, but for MediaWiki namespaces.
 my @tracked_namespaces = split(/[ \n]/, run_git("config --get-all remote.${remotename}.namespaces"));
+for (@tracked_namespaces) { s/_/ /g; }
 chomp(@tracked_namespaces);
 
 # Import media files on pull