Auto creation of taxonomies of multiple categories and categories with HTML

The attached patch will handle the auto creation of taxonomies of multiple categories and categories with HTML. For example, the MyDD feed http://feeds.feedburner.com/mydd returns categories that look like this:

<category>&lt;br /&gt;Tags: &lt;a href="http://www.mydd.com/tag/primary%20elections"&gt;primary elections&lt;/a&gt;, &lt;a href="http://www.mydd.com/tag/President%202008"&gt;President 2008&lt;/a&gt;, &lt;a href="http://www.mydd.com/tag/Democrats"&gt;Democrats&lt;/a&gt;, &lt;a href="http://www.mydd.com/tag/polls"&gt;polls&lt;/a&gt; (&lt;a href="http://www.mydd.com/tag"&gt;all tags&lt;/a&gt;)</category>

With this patch, autotaxonomy strips out the unnecessary HTML and creates terms for "primary elections", "President 2008", "Democrats", etc. Without this patch, autotaxonomy creates ugly looking categories that are pretty much unusable.

This patch also replaces multi-word taxonomies with two taxonomies. For example, if the category is:

<category>Democrats, Elections</category>

It creates two categories. However if the category is:

<category>2008 Elections</category>

It creates only one category. The key is the comma separator.

This patch has no effect on categories without HTML.