Add failing test case for installing when there are symlinks to directories
Keep symlinks as symlinks when installing

Without this, "pip install" crashes when encountering symlinks that
point to external paths. The culprit is "shutil.copytree()", which
throws an error in such cases if the "symlinks" parameter is not set to
"True".

This fixes #1006.
Add symlinks=True to copytree invocation so that tests pass in Python 3
Merge pull request #1311 from mwilliamson/py3-symlinks

Fix: "pip install ." fails on Python 3.3 (with symlinks in local directory)