* tests/common.c (temp_dir_setup): Fail the test if mkdtemp fails.
* lib/pipeline.c (argstr_get_word, pipeline_free): Remove
  unnecessary tests before freeing pointers.
* lib/pipeline-private.h (struct pipeline): Make want_infile and
  want_outfile non-const.
* lib/pipeline.c (pipeline_join): Take copies of p1->want_infile and
  p2->want_outfile.
  (pipeline_want_infile): Take a copy of file.
  (pipeline_want_outfile): Likewise.
  (pipeline_free): Free p->want_infile and p->want_outfile.
* NEWS: Document this.