named atomic test spams /tmp

[Daniel Shahaf]

named_atomic-test doesn't clean up its tempfiles:

% find /tmp -mtime -1
/tmp
% ../runctest subr named_atomic
...
% find /tmp -mtime -1
/tmp
/tmp/svn-uOqtyy
/tmp/svn-BXJBbj
/tmp/svn-JoeKO3
% 

At a guess those are the three svn_io_file_del_none files from
init_test_shm().  Can someone ensure they're removed?

Thanks.