Atom feed entry updated field should use get_post_modified_time, not get_post_time

[lapcat]

The file wp-includes/feed-atom.php in WordPress 2.2 contains code for generating an Atom feed. (In WordPress 2.0, the code is in the file wp_atom.php.) Here are lines 34 and 35 from feed-atom.php:

		<updated><?php echo get_post_time('Y-m-d\TH:i:s\Z', true); ?></updated>
		<published><?php echo get_post_time('Y-m-d\TH:i:s\Z', true); ?></published>

Both the updated and published fields use the function get_post_time, so the date output will end up being the same. Line 34 should be replaced with the following:

		<updated><?php echo get_post_modified_time('Y-m-d\TH:i:s\Z', true); ?></updated>

I've been using this modification in ​my own blog for 10 months will no ill effects. Feed readers such as ​Vienna, which I am a developer for, can correctly parse this updated date information and respond accordingly.

See the ​Atom API for reference on the updated entry field.

Patch for wp-includes/feed-atom.php

(In [6093]) Make the atom feed updated field actually tell you when the post was updated. Fixes #4816 props lapcat.