Nope, no missing dependencies, and during my trials I specified all --enable-stuff (except debug) build options.
Subsequently, I waded back through the sourceforge request+patch tickets, the alternative branches (and forks) at github, and cherrypicked all the patches which seemed useful -- not just in terms of rotated text -- and never did arrive at being able to render a wide, horizontally stacked taskbar presentation within a left-docked fluxbox panel. Maybe, due to wishful thinking on my part, I just misinterpreted the changelog comment(s).
I still don't understand the meaning of those changelog comments. After the 1.7.3 "fix", what was the intended result? Within a given taskbar container (button), when the panel is vertically oriented, should we expect to see
? ? ?
Anyhow, I moved on, and achieved a "solution" by hacking fbpanel .
It supports vertical orientation, can be configured to individually exclude tray and clock and...
(other whizmos which are redundant with those provided by fluxbox panel and/or conky)
...and I relaxed its hardcoded 192px maxwidth constraint.
After wrestling with code for many hours, I'm laughing at self because the real-world content of my "nice wide autohiding tasklist" often provides less-than-ideal labelnames like
[ leafpad /home/bartholemew/longassed/path/to/some/Documents/projectX/iwannapony.txt ]
[ Mozilla Firefox ]
[ Find ]
[ rules ]