Deprecate in_category in favor of has_category

[Otto42]

#12526 introduced has_category. There was some patches there which did and did not deprecate in_category.

End result is that they're now both in category-template.php, doing the exact same thing (serving as a wrapper to has_term).

I think we need some naming consistency here. Deprecate one or the other of them in 3.2, perhaps.

There was some discussion on this, possibly in IRC... Basically, in_category() is such an old function used by so much code, simply renaming it for pure consistency will be annoying, especially for reviewed themes. We're evil, but not that evil. Introducing has_category() but not deprecating is_category() seemed like a fine idea at the time.

Ah.. well, in that case, it might be worth making one call the other in order to avoid duplicated code and/or to prevent future changes from not happening to both of them.

Also, might be worth switching twentyten to use has_category.