Add validation to prevent terms > 255 characters

1) Have a content_taxonomy_autocomplete field, multivalue, maxlength > 255.
2) Add a word > 255 chars
Vivamus sed lacus at tellus condimentum eleifend vel in justo Phasellus sapien est; semper non faucibus sed pellentesque at libero Vestibulum sit amet urna magna Lorem ipsum dolor sit amet consectetur adipiscing elit Suspendisse a est et nisi pellentesque ultrices a ut ante Aliquam ac mi sapien Vivamus sodales sapien quis elit blandit ullamcorper dictum lectus vulputate Fusce ut eros vitae libero venenatis cursus
3) Click save
4) Word truncated

(BTW, according to my spell check, 'cutted' is not the word, however updated description to remove that)

Corresponding core issue #1329682: Tagging fields truncates terms > 255 characters without warning