Fix tutorial with link to filer installation instructions
Merge pull request #1911 from yakky/feature/doc_filer_fix_24

Fix tutorial with link to filer installation instructions
Fixes #1004
Adding some information on using pip and virtualenv

Backport to 2.4 of #1908
Backport minor installation rewording to 2.4
Merge pull request #1923 from yakky/feature/virtualenv_doc_backport

Backport of #1908 installation doc
Test for #1919
Cache-busting in show_placeholder if page in preview mode
Merge pull request #1927 from yakky/feature/show_placeholder_uncached_preview

Test and fix for #1919
Merge branch 'support/2.4.x' of github.com:benjaoming/django-cms into develop