Change the built-in wp_caption & caption function to be XHTML compliant

[PoPSiCLe]

The built-in function for creating wp_captions and captions to images is at best flawed, as it uses <div>'s to contain the container for the image and image-text. When these div's are placed inside <p>-tags, it breaks validation, and may also introduce other issues, based on CSS and other plugins.

Hence, the whole function should have a quick rewrite.

[PoPSiCLe]

This is a code-example taken from my theme's functions.php-file, hence it's a replacement function, it should "pop in" directly and replace the original one, though. CSS is included

[ocean90]

#12097