FreeFEm++ cannot find its libraries / plugins

[Michel Kern]

It seems that FreeFem++ plugins (and library files) are installed in the wrong location:

with the file "load.edp" containing a single line:
load iovtk

Typing
Freefem++ load.edp
gives
-- FreeFem++ v4.9 ( - git no git)
 Load: lg_fem lg_mesh lg_mesh3 eigenvalue
    1 : load "iovtk"
Load error: iovtk
  fail:
 dlerror : /usr/lib/ff++/4.9/lib/iovtk.so: cannot open shared object file: No such file or directory
list prefix: './' '/usr/lib/ff++/4.9/lib/' list suffix: '' , '.so'

The file iovtk.so exists in two locations:
/usr/lib/freefem++/iovtk.so
/usr/lib/freefem++/mpi/iovtk.so

However, FreeFem++ was looking for /usr/lib/ff++/4.9/lib/iovtk.so
and in general FreeFem++ support files should be in /usr/lib/ff++/4.9

This is on jammy (22.04),
freefem++, libfreefem++ and libfreefem++-dev all from 4.9+dfsg1-2build1