If you happen to accept my pull request for auto-complete/popup-el#29, I'd like to propose putting in a customizable value for limiting the auto-complete width. It just adds a variable ac-max-width that sets a maximum width for the auto-complete popup.
Adding max width for auto-complete based on popup.el's max width limits
Looks good. But Travis failure here is essential. We should update lib/popup in this pull request before merging this. And updating lib/popup requires pulling auto-complete/popup-el#29 first.
Adding custom variable 'ac-max-width' same as #202
And submodule of popup-el is updated for test.
Add customizable variable 'max-width' same as #202