After installing phoronix-test-suite, adding "/" to php’s open_basedir and enabling a few extensions (zip, openssl) as recommended by the post-install message and PTS itself, and launching a test:

phoronix-test-suite benchmark 1408092-KH-1408099KH43

I’m getting this warning for every download:

[NOTICE] curl_setopt(): CURLOPT_FOLLOWLOCATION cannot be activated when an open_basedir is set in pts_network:102

It works fine as long as there is no redirection, but fails for xonotic:

pts/xonotic-1.3.1:
Test Installation 5 of 13
1 File Needed [993 MB / 21 Minutes]
Downloading: xonotic-0.7.0.zip [993MB]

[NOTICE] curl_setopt(): CURLOPT_FOLLOWLOCATION cannot be activated when an open_basedir is set in pts_network:102
Estimated Download Time: 21m .......................................
MD5 Failed: http://dl.xonotic.org/xonotic-0.7.0.zip
Try downloading the file again (Y/n):

(Downloading with Firefox works fine but redirects to another URL.)

A search in the phoronix forum returned this thread:
http://www.phoronix.com/forums/showthread.php?98426-PTS-5-0-1-Push-Notifications-Improves-Arch-Linux-New-Features

where a user reports this same problem, and Michael Larabel (author of PTS) replies:
"You could just comment out the open_basedir line in the php.ini, that's generally what I do."

I have tried to comment-out open_basedir and it did solve the downloading problem of xonotic.