about override in styles

[yiminghe]

steps: 1.open www.ckeditor.com/demo 2.switch to source mode,input html:

<p>
	12345678<font style="background-color: rgb(130, 130, 130);">xyzabcd</font>9012345678</p>

3.switch to wysiwyg mode and place cursor between 'y' and 'z', then click background button , select '自动'

4. expected:

'xyzabcd' does not have background-color.

actual result :

unchanged

5.select '8xyzabcd9' ,then click background button ,select red color

6. expected :

generate code :

<p>
	1234567<span style="background-color: rgb(255, 0, 0);">8xyzabcd9</span>012345678</p>

actual code (too bloated):

<p>
	1234567<span style="background-color: rgb(255, 0, 0);">8</span><font style="background-color: rgb(130, 130, 130);"><span style="background-color: rgb(255, 0, 0);">xyzabcd</span></font><span style="background-color: rgb(255, 0, 0);">9</span>012345678</p>

ps:in trunk ,result is error :

<p>
	1234567<span style="background-color: rgb(255, 0, 0);">8<font style="background-color: rgb(130, 130, 130);">xyzabcd</font>9</span>012345678</p>

ps2: i provide a patch for trunk, add consideration about override element's style

[Krzysztof Studnik]

DUP of #6977