OK, I finally figured it out myself.  It was not an issue with my directory being setup as an application - as it turns out, if that was the problem I would not have even gotten the error.  It was not a problem with my web.config file, as I knew.  And, it was not a problem with permissions.

I got this error because the several of the dll files in the bin directory, including the primary DotNetNuke.dll file, had only partially uploaded.  Thus the file was there but was half it's correct size and therefore corrupt (incomplete), creating the same effect - the scripts couldn't access the file, thus those variables were not declared.

I also learned from my local install that the scripts that run after the database connection is successfully tested require dbo permissions.  I had gotten the idea from something I had read in the documentation that dbo permissions was not required as long as you put in the alternate username in the "databaseOwner" setting in web.config.  But that did not work for me.  Luckily my hosting company was willing to grant my user dbo rights.

Another post I found suggested that after the database install scripts ran but before I hit next, that I would manually have to grant my user all of the aspnet roles it created.  I checked and found this to be the case - the roles were there but by user was not assigned to the roles, despite my dbo clearance.  I set them manually before proceeding.  Thanks to whoever posted that.

Lastly, the 4.4.1 documentation implies that the development.config file should be used in place of release.config for medium trust environments.  However, it appears that the 4.5.1 release.config file already has the requirePermission="false" entries in it, so it seems to me that the 4.5.1 package no longer needs the development.config file.