Merge branch 'master' of git://github.com/yiisoft/yii2
It is not required by default when you set the "when" attribute
Fixes #4519: `yii\base\Model::isAttributeRequired()` should check if the `when` option of the validator is set
Update intro-upgrade-from-v1.md
Merge pull request #4523 from littlefuntik/patch-1

Update intro-upgrade-from-v1.md
Fixes #4497: Bad Request, Unable to verify your data submission
Update translation-teams.md
Merge pull request #4524 from mbman/bugfix-4497

Fixes #4497: Bad Request, Unable to verify your data submission
Fix Russian translation
Merge pull request #4527 from mickgeek/master

Fix Russian translation
Added encoding to StringHelper::byteSubst() fallback
length arg of byteSubstr is now optional
avoid random test break
Do allow PHP5.6 to fail anymore

as it is in RC phase now we should be able to report bugs if they occur.
fixed HHVM test break
Update CHANGELOG.md
Update CHANGELOG.md
Update yii.activeForm.js

Refactored
Update input-validation.md

Updated guide
add page start-forms.md