[PHP-DEV] Allow sleep() to accept non-integer values

[Michael Voříšek - ČVUT FEL]

Hi everyone, 

I am the author of https://github.com/php/php-src/pull/5961 , please
provide feedback. 

All details should be in the description, also, please advise if we can
consider it as a small change not requiring RFC as Nikita proposed in
his comment. 

With kind regards / Mit freundlichen Grüßen / S přátelským pozdravem,
Michael Voříšek