Bug 707311 - Tax Invoice fails to open when using guile 2 - addendum

Make it also work with guile 2 in non-compiled mode

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23459 57a11ea4-9604-0410-9ed3-97b8803252fd
Improve cond-expand/eval-when usage based on feedback from the guile developers

Basically two things:
- whenever eval-when is used, the expand keyword should be added (not yet documented)
- eval-when is not needed for use-modules, because use-modules is a macro that performs the eval-when by itself

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23460 57a11ea4-9604-0410-9ed3-97b8803252fd