"Too many open files" error nn macOS (plus fix)

duplicity 0.7.10
Python 2.7.10
macOS 10.12.4
target filesystem: hfs+

On macOS, the tempfile.TemporaryFile call erroneously raises an IOError exception saying that too many files are open. This causes restores to fail randomly, after thousands of files have been restored.

The following patch seems to work around the problem:

*** /Users/howie/duplicity-0.7.10/duplicity/patchdir.py 2015-09-10 09:03:43.000000000 -0400
--- patchdir.py 2017-05-09 14:27:38.000000000 -0400
***************
*** 496,502 ****
              See https://bugs.launchpad.net/duplicity/+bug/670891 for discussion
              of os.tmpfile() vs tempfile.TemporaryFile() w.r.t. Windows / Linux.
              """
! if sys.platform.startswith(('cygwin', 'windows')):
                  tempfp = os.tmpfile()
              else:
                  tempfp = tempfile.TemporaryFile(dir=tempdir.default().dir())
--- 496,502 ----
              See https://bugs.launchpad.net/duplicity/+bug/670891 for discussion
              of os.tmpfile() vs tempfile.TemporaryFile() w.r.t. Windows / Linux.
              """
! if sys.platform.startswith(('cygwin', 'windows', 'darwin')):
                  tempfp = os.tmpfile()
              else:
                  tempfp = tempfile.TemporaryFile(dir=tempdir.default().dir())