Add a test for image node teasers

Issue Summary

Here's a extra test that checks that the image thumbnail shows in the node teaser.
Needs the admin nodes permission adding so that the user can promote the image node (in case the site is set with images not promoted by default).

Sorry I can't do a patch -- CVS patch is going mental on me and showing the entire file as the diff, even after changing line endings.

@line 16, change:
// User to create images.
$this->web_user = $this->drupalCreateUserRolePerm(array('create images', 'view original images', 'edit own images', 'edit images', 'administer nodes'));

@line 38, change:
// Create an image.
$edit = array(
'title' => $this->randomName(),
'body' => $this->randomName(),
'files[image]' => realpath($this->image),
'promote' => TRUE,
);

@line 64, add:
$this->drupalGet('node');
$this->assertWantedPattern('|]+?' . $node->images['thumbnail'] . '[^>]+?>|', $this->drupalGetContent(), 'Image thumbnail is on the front page teaser. %s');