store: exclude `undo.` nodemap's file from `walk`
There are "temporary" local file that we should not be transfered by `walk` user
like local clone and stream clone.
This fix the small issue that the new tests highlighted.
Differential Revision: https://phab.mercurial-scm.org/D10482
#require docutils gettext
$ $TESTDIR/check-gendoc de
checking for parse errors
Die Dateien werden dem Projektarchiv beim n\xc3\xa4chsten \xc3\x9cbernehmen (commit) hinzugef\xc3\xbcgt. Um dies vorher r\xc3\xbcckg\xc3\xa4ngig zu machen, siehe:hg:`forget`. (esc)
warning: please have a space before :hg: