CRM-19813 - CRM_Utils_Hook - Don't allow conflicts in property names

CRM-19813 - CRM_Utils_Hook - Don't allow conflicts in property names

Traditionally, the names of the hook parameters were advisory/aesthetic.
With the introduction of GenericHookEvent, they become first class symbols
-- and they can theoretically conflict with properties of `GenericHookEvent`
or `Event`.  In particular, the parameter `$name` conflicts with
`Event::$name` in Symfony 2.x.