Fixed {% render_plugin %} example

The instance.child_plugins reference is not correct, it should be instance.child_plugin_instances.
Merge pull request #2045 from andreiavram/patch-1

Fixed {% render_plugin %} example
Fixed: Unable to add plugin

Fixes bug which made it impossible to add plugins, with placeholder.pk>=1000. Reason was, that placeholder.pk got a thousand separator.
Merge branch 'master' of https://github.com/divio/django-cms
Merge pull request #2303 from jrief/fix-iframeheight

Primary key in setiframeheight is not unlocalized
In get_placeholder_conf check value against None to allow '0' as a valid configuration value
Merge pull request #2368 from yakky/feature/check_noneness_24

Backport of #2365 to 2.4
reversion 1.8+ compatibility
Add reversion 1.8 to django 1.5 tests
Merge pull request #2381 from yakky/feature/fix_reversion_24

Feature/fix reversion 24
Merge branch 'support/2.4.x' of https://github.com/divio/django-cms into 2.4.x