Check if tcl/tk files/dirs exist before copying

[nodirt]

Copying fails if tcl/tk files are not there. This happens in our setup,
where Python 2.7.6 is used.
Check if they exist before copying.

[nodirt]

cc @techtonik

[techtonik]

How come that they are not there? I'd be against workarounds for hacked installations unless there is a really good reason.

Also, https://www.cvedetails.com/vulnerability-list/vendor_id-10210/product_id-18230/version_id-160977/Python-Python-2.7.6.html

[nodirt]

We don't use tcl/tk in our installation and prefer to deploy it to thousands of our machines

[techtonik]

@nodirt I am interested to use the socket vulnerabilities on thousands of your machines. I don't mind against the change, especially if PyPA group gets some funding as a result of incorporating this change (because I don't have write access). Just curious what do you do with Python 2.7.6 there?

[carsonyl]

I support this change. It's necessary to check that the tcl/tk directories being copied actually exist, because they're an optional install item. In my case, I haven't installed it on my Python 2.7.11 and 3.5.1, and my Tox stopped working due to the change in #888.

[techtonik]

It's necessary to check that the tcl/tk directories being copied actually exist, because they're an optional install item

@rbcarson good point.

[nodirt]

@techtonik you are right, we should update Python. Turned out it has nothing to do with this PR. Even with the latest version we still prefer not to deploy TCL/TK.

[techtonik]

I see that even my fix for Python 3.3- #926 was not merged, so unless somebody finds a way to sponsor virtualenv development, it may not be fixed any time soon.

[nodirt]

@dstufft it's been a week. Please take a look. Alternatively, please take a look at #933
We can't update to the new virtualenv because of this

[Ivoz]

This change should be obsoleted by #937, cheers