Synonyms are generally made for two existing and well-established tags that mean the same thing. For example, csharp and c# may be synonymed. It is of no use to synonym a nonexistent tag, even when the non-existent one is easier to type. Once it is well-used, the synonymization may be done, but both have to be pretty powerful tags.
With that said, do not spend your time retagging autohotkey to ahk. If people use it often, then it will be something that can be brought to the table again. There is also no need to ask for it to be created since IMHO the current tag is fine.
Tag synonyms are not used as a shortcut for the main tag; they are used when users keep using two different tags for the same purpose. Suppose that enough users use drupal7 instead of drupal-7; if drupal7 is continuously used, and it is rather impossible to re-tag the questions using it because there is always somebody using it in new questions, then drupal7 is merged with drupal-7, and made a synonym of drupal-7.
Making a tag synonym of a longer one doesn't make sense. First off, there isn't the need to completely write a tag as there is autocomplete that suggests you the tags that you probably want to use. Secondly, some tags could be used as short version of more than one tag; it would be rather difficult to decide for which tag it should be a synonym.
The second screenshot proves what Mat said in his comment: Write otk when you are adding a tag to a question, and you will get autohotkey as first suggestion.
As you notice in the last screenshot, drupal7 has been really merged with drupal-7, and made its synonym, but it didn't happen because drupal7 was a shortcut for drupal-7. In fact, by the time you write drupal7, you could also write drupal-7.