Ticket #3111: configurable selection reset on CK_Store.

In mc-4.7.x.x selection was reset on CK_Store (copy to buffer).
In mc-4.8.x (4.8.11 and older) it is not.

Now this behavior is configurable using editor_drop_selection_on_copy
key in the ini file.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Merge branch '3111_mcedit_reset_selection'

* 3111_mcedit_reset_selection:
  Ticket #3111: configurable selection reset on CK_Store.