deferred validation

Added support of deferred to ```ActiveForm``` validation.
deferred validation

Added support of deferred validation.
Update yii.activeForm.js

remove empty message arrays
Update yii.activeForm.js
Update input-validation.md
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
Fix signature validation
Using of `MongoCollection::createIndex()` provided
Merge pull request #4539 from mickgeek/master

Fix signature validation
- Enh #4520: yii\caching/MemCache.php add sasl support (xjflyttp)
Merge pull request #4542 from xjflyttp/4520-cache-memcache-sasl-support

- Enh #4520: yii\caching/MemCache.php add sasl support (xjflyttp)
minor fixes [skip ci]