Clarify the return value of wp_generate_tag_cloud()

[SergeyBiryukov]

Background: #27413

The function description says that it only returns a string:
tags/3.8.1/src/wp-includes/category-template.php#L604​

However, it can also return an array, depending on format argument:
tags/3.8.1/src/wp-includes/category-template.php#L680​

It also returns null if $tags argument is empty:
tags/3.8.1/src/wp-includes/category-template.php#L626​

I think it should only return a string or an array, for consistency with the format argument.

[DrewAPicture]

The verbiage of return $return is not my favorite, even though it's already in use at the end of the function. Would be nice if it were something like $output instead.

That said, I agree about returning only a string or array.

[SergeyBiryukov]

27487.2.patch​ changes the variable to $output.

[DrewAPicture]

Works for me.

27487.3.patch​ fixes the hook docs to account for the mixed type on $output.

[nacin]

In 27708:

Clarify the return value of wp_generate_tag_cloud().

props SergeyBiryukov, DrewAPicture.
fixes #27487.

[nacin]

return $return may be a bit weird, but return $output isn't any more descriptive. I've left it alone to reduce churn.