[plt-scheme] where to put extensions?

[Sebastian H Seidel <Sebastian.H.Seidel@hno.med.uni-giessen.de>]

If distributing a collection consisting of an extension and
module^A.ss that depends on module^B that is provided by the
extension:

module^A.ss  <==requires==  module^B  <==provided-by==  extension.dll

a) Where should I put the extension? plt-home? collection-directory?
b) How can I make module^A load the extension and require module^B?

If that's not possible, the user of module^A has to load the extension
himself before he can use module^A.
How can he do so conveniently? Is there any command that does not rely
on an absolute path-string? Or how may that been done somewhat
setup-independently?

Assuming there is no installation-independent standard way to load an
extension, I might eventually define my own extension-loader.
Therefore, I need to compute the absolute path-string to plt-home.
How?
- (find-system-path 'exec-file) ?
- (find-system-path 'init-dir) ?
- something else?

Sebastian