Gnc-Prefs: migrate 24hour_clock preference and fix the code
so it actually works. (It's not actively used though in GnuCash)

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23236 57a11ea4-9604-0410-9ed3-97b8803252fd
Gnc-Prefs: migrate extra_toolbuttons preference (business option)

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23237 57a11ea4-9604-0410-9ed3-97b8803252fd