In previous WP versions, if you entered text in the optional "Excerpt" box, then the manually-entered excerpt would appear on index.php; if you left the "Excerpt" box blank, then the whole post would appear. I don't want to use the <!--more--> tag, because I like the option of placing in the "Excerpt" box text that doesn't necessarily appear in the actual post when viewed in its entirety ... and I also don't want to replace the_content() with the_excerpt(), because I'm not interested in having excerpts appear for all entries.
In other words: it wasn't broken until someone "fixed" it in the latest version. How do I get it back to how it was?