Greek spell checking swaps final sigma for median sigma ('ς' vs 'σ').

What steps will reproduce the problem?
1. Download http://ftp.vim.org/vim/runtime/spell/el.utf-8.spl in your
   .vim/spell directory.
2. Open a new file and enable Greek spell checking by executing
   :set spell spelllang=el
3. Write any word that ends in a final sigma (ς), with an intentional spelling
   error (no accent used), for example "κοσμος".
4. Request a suggestion for that word by pressing z=

What is the expected output?
The word κόσμος

What do you see instead?
κόσμοσ

Note: That all suggsted words only include media sigma and never final sigma.
On top of that if the input word is ending in a media sigma, vim fails to
identify this as a spelling error.

What version of the product are you using? On what operating system?
Vim version: VIM - Vi IMproved 7.4 (2013 Aug 10, compiled Jan  2 2014 19:39:32
OS: Ubuntu 14.04.

Any information on how to solve this bug is appreciated.

Original issue reported on code.google.com by dpa...@chromium.org on 20 Dec 2014 at 10:08

Bluelich / vim

Greek spell checking swaps final sigma for median sigma ('ς' vs 'σ'). #299