pip install . confused by _trial_temp

[nejucomo]

For some reason pip install . in a new virtualenv, with a dirty working directory does a lot of useless work and gets confused by _trial_temp.

It should ignore _trial_temp.

Here's a transcript:

$ pip install .
Unpacking /home/n/sandbox/lafs-tools/tahoe-lafs
Cleaning up...
Exception:
Traceback (most recent call last):
  File "/home/n/virtualenvs/tahoe-summit/local/lib/python2.7/site-packages/pip/basecommand.py", line 134, in main
    status = self.run(options, args)
  File "/home/n/virtualenvs/tahoe-summit/local/lib/python2.7/site-packages/pip/commands/install.py", line 236, in run
    requirement_set.prepare_files(finder, force_root_egg_info=self.bundle, bundle=self.bundle)
  File "/home/n/virtualenvs/tahoe-summit/local/lib/python2.7/site-packages/pip/req.py", line 1092, in prepare_files
    self.unpack_url(url, location, self.is_download)
  File "/home/n/virtualenvs/tahoe-summit/local/lib/python2.7/site-packages/pip/req.py", line 1234, in unpack_url
    return unpack_file_url(link, loc)
  File "/home/n/virtualenvs/tahoe-summit/local/lib/python2.7/site-packages/pip/download.py", line 420, in unpack_file_url
    shutil.copytree(source, location)
  File "/usr/lib/python2.7/shutil.py", line 208, in copytree
    raise Error, errors
Error: [('/home/n/sandbox/lafs-tools/tahoe-lafs/_trial_temp/cli/Cp/dangling_symlink_vs_recursion/dir/link', '/home/n/tmp/pip-hm4RZH-build/_trial_temp/cli/Cp/dangling_symlink_vs_recursion/dir/link', "[Errno 2] No such file or directory: '/home/n/sandbox/lafs-tools/tahoe-lafs/_trial_temp/cli/Cp/dangling_symlink_vs_recursion/dir/link'"), ('/home/n/sandbox/lafs-tools/tahoe-lafs/_trial_temp/allmydata.test.test_cli/Backup/test_ignore_symlinks/jCgDjH/home/foo2.txt', '/home/n/tmp/pip-hm4RZH-build/_trial_temp/allmydata.test.test_cli/Backup/test_ignore_symlinks/jCgDjH/home/foo2.txt', "[Errno 2] No such file or directory: '/home/n/sandbox/lafs-tools/tahoe-lafs/_trial_temp/allmydata.test.test_cli/Backup/test_ignore_symlinks/jCgDjH/home/foo2.txt'")]

Storing complete log in /home/n/.pip/pip.log

[daira]

Duplicate of #2210.