Minor tweaks to pull down menus (and the tab size menu)

The first commit is related to our previous conversion concerning pull down menus. I noticed the tab size menu was exhibiting the same behavior where the "title" item would appear disabled after activating the menu. Although not completely necessary, I decided to go ahead and assign the action `NULL` to all instances where a `nop:` was used for the "title" item in pull down menus. This way we do not need to worry about whether `validateMenuItem` is called.