MANPL gives page length - undocumented; may disappear again

[But brobison@ecst.csuchico.edu likes it and says:
it allows one to do something like:

export LINES
export MANPAGER='less -i'
export MANPL='$(perl -e "print ($LINES - 1) / 6, \"i\";")'
]

hman does not use LANG

Integrate Olaf's `cache manager' patch ?
Adding additional processes and communication makes the
system much more fragile. (And might fail on CYGWIN32.)
Are there known security problems in the present setup?