pip won't ignore system-installed files

[Neal Becker]

IIUC, it is perfectly legitimate to do install into --user to override system-
wide installed modules.  Thus, I should be able to do:

pip install --user --up blah

even though there is already a package blah in 
/usr/lib/pythonxxx/site_packages/...

But even with -I (ignore installed) switch, pip fails:

pip install --user --up -I matplotlib
...
 Installing collected packages: matplotlib, numpy, python-dateutil, tornado, 
pyparsing, nose, six
  Found existing installation: matplotlib 1.2.0
    Uninstalling matplotlib:
Exception:
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/pip-1.2.1-
py2.7.egg/pip/basecommand.py", line 107, in main
    status = self.run(options, args)
  File "/usr/lib/python2.7/site-packages/pip-1.2.1-
py2.7.egg/pip/commands/install.py", line 261, in run
    requirement_set.install(install_options, global_options)
  File "/usr/lib/python2.7/site-packages/pip-1.2.1-py2.7.egg/pip/req.py", line 
1162, in install
    requirement.uninstall(auto_confirm=True)
  File "/usr/lib/python2.7/site-packages/pip-1.2.1-py2.7.egg/pip/req.py", line 
495, in uninstall
    paths_to_remove.remove(auto_confirm)
  File "/usr/lib/python2.7/site-packages/pip-1.2.1-py2.7.egg/pip/req.py", line 
1492, in remove
    renames(path, new_path)
  File "/usr/lib/python2.7/site-packages/pip-1.2.1-py2.7.egg/pip/util.py", line 
273, in renames
    shutil.move(old, new)
  File "/usr/lib64/python2.7/shutil.py", line 302, in move
    os.unlink(src)
OSError: [Errno 13] Permission denied: '/usr/lib64/python2.7/site-
packages/matplotlib-1.2.0-py2.7.egg-info'

Can we please fix this?