SCAYT attributes needs to be filtered on paste

[SpellChecker.net]

This is the follow-up of bug #6588.

Pasted text markuped with SCAYT in one language is not re-checked with SCAYT if another spellchecking language is selected in editor.

Steps to reproduce:

1. Open 2 pages of http://ckeditor.com/demo, enable SCAYT for both of them.
   
2. In first window in SCAYT's menu select "French" as spellchecking language, wait for misspelled words to be underlined.
   
3. Select all text from the first window and paste it into second one.

Actual result:
Correct words in English are still shown as misspelled.

Expected result:
On pasting old SCAYT markup is removed, new markup is applied after processing text.

[SpellChecker.net]

Here is the part of ​http://dev.ckeditor.com/attachment/ticket/6588/6588_4.patch. Filtering SCAYT attributes should be included to fix this issue.

[garry.yao]

Fixed with [6439].