SIDEBAR PROBLEM SOLVED
Kathy Kinsley figured out my problem and, alas, it was one of my own creation. In trying to install the compression code, I inadvertanly overrode the .htaccess file because, since my FTP program doesn’t display files with a leading “dot,” I presumed I didn’t have one on the server. Apparently, there was some rather important stuff on the “old” .htaccess file which has now been restored.
The fact that this coincided with HostingMatters screwing around with their php protocols, with which this problem is loosely associated, added a bit of confusion to the whole thing.