If you remember the thread I started a few weeks back on my inability to install 1.4, I finally got it completed. I think the problem was that I had created a sub-domain for Piwik and as such did not port the /piwik folder but rather installed the files directly under the domain. Some pieces of the Piwik code did not like this. A reinstall of 1.4 with that folder intact fixed the issue. Perhaps this needs to be documented and made more visible or, in the alternative, when the check is run for server requirements perhaps the existence of the install path needs to be double checked.
Then I had a problem with the upgrade to 1.5. Piwik (specifically /Zen/session.php) looks for a session ID file in public_html/cgi-bin/tmp. I had accidentally deleted my public_html and when I recreated the folders I made what seems to be a big typo; I make a folder named cgi_bin instead of cgi-bin (underscore vs hyphen). That caused all sorts of problems until I figured out what I had done. Perhaps presence of the session file needs to be double checked as well.
Now that the shockingly high level of user incompetence has been cured, everything is working as expected. Thanks to all who tried to help.