Support Excerpts

Some of the testimonials used are real long, and I want to show the full one by default, but simply supporting excerpts in the post type allows me to do:

```
/* Show Excerpt in Testimonials Widget */

function woo_exchange_excerpt($post) {
	global $post;
	if ( $post->post_excerpt && !is_page('Customer Testimonials') ) {
		return $post->post_excerpt;
	} else {
		return $post->post_content;
	}
}

add_filter( 'woothemes_testimonials_content', 'woo_exchange_excerpt', 10, 2 );
```