[FIX] installer: Fix language selector which was failing as the cache was being cached afterwards on every page. So move cache clearing to only happen after system requirements page, but before language and other prefs have been set up.

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/11.x@46374 b456876b-0849-0410-b77d-98878d47e9d5