Faster theme searching. Only calculate what is necessary -- if the theme...

Faster theme searching. Only calculate what is necessary -- if the theme doesn't have all of the features, bail. If a word matches a tag or header, jump to the next word, we don't care how many times it matches. see #20103.

git-svn-id: https://core.svn.wordpress.org/trunk@20027 1a063a9b-81f0-0310-95a4-ce76da25c4cd