Revert "Revert "Add specific condition for back-key handle""

Revert "Revert "Add specific condition for back-key handle""

  * Note: ewk_view_text_selection_clear() API is now available in RSA webkit.

[Issue#]   P130829-05787
[Problem]  Long press on the text to enter text-selection mode.
           Back-key is working to history back or send tizenhwkey event to Application even current mode is text-selection mode.
[Cause]    Elementary is called back-key callback both webkit and wrt.
[Solution] WRT calls "ewk_view_text_selection_clear" before handle back-key.
           If return value is "EINA_TRUE", back-key is handled by webkit.
           As back-key event is handled by webkit, WRT doens't need to handle back-key.
           In case of return value is "EINA_FALSE", WRT should handle back-key.
           History back or dispatch tizenhwkey event to application.

[SCMRequest] N/A

Change-Id: I7d96d3b2ea38a42e4e8d2746f27137cfcf1bbc94