Issue 7880: sysconfig does not like symlinks

Here's the traceback, I'll look at the problem asap

'import site' failed; traceback:
Traceback (most recent call last):
  File "/MacDev/svn.python.org/python-trunk/Lib/site.py", line 530, in <module>
    main()
  File "/MacDev/svn.python.org/python-trunk/Lib/site.py", line 509, in main
    addbuilddir()
  File "/MacDev/svn.python.org/python-trunk/Lib/site.py", line 118, in addbuilddir
    s = "build/lib.%s-%.3s" % (get_platform(), sys.version)
  File "/MacDev/svn.python.org/python-trunk/Lib/sysconfig.py", line 577, in get_platform
    cfgvars = get_config_vars()
  File "/MacDev/svn.python.org/python-trunk/Lib/sysconfig.py", line 402, in get_config_vars
    _init_posix(_CONFIG_VARS)
  File "/MacDev/svn.python.org/python-trunk/Lib/sysconfig.py", line 255, in _init_posix
    raise IOError(msg)
IOError: invalid Python installation: unable to open /usr/local/lib/python2.7/config/Makefile (No such file or directory)