Merge pull request #2421 from yiiframework-com-ua/master

Removed unnecessary PHPDoc property
Inconsistently insecure

Why use a strong random number generator in one place, but not another? I know salts have no cryptographic security requirement, but collisions are less likely if you use one.
Merge pull request #2422 from sarciszewski/patch-1

Inconsistently insecure
added back fallback mechanism for generating salt.
Added helpers.md
Fixed test break.
fixed test break.
minor doc improvement.
Fixed test break.