racket/gui cocoa: fix `list-box%' visble-cell calculations

There were especially problems with header columns, but
also intercell spacing was not taken into account.

Merge to v5.3.4
pkg/lib: clean up names and package-scope parameter

More consistent exported names and parameters that better match the
three scope choices (installation, user, or shared) --- cleaning up
after myself.
pkg/lib: lock clean-up, and add `path->pkg'

Make the installed-package database lock reentrant, change some
functions to take the lock, and fix the documentation on when a
lock is expected to be taken outside of functions.
ffi/com: repairs for parameterized-property setting and for date values

Merge to v5.3.4