Safe to make liqueur from tomato vines?
This would be a really, really bad idea. The alkaloid compounds that make nightshades toxic can be toxic even at low levels, and a few of them are specifically alcohol soluble. This means that while chomping down on a tomato leaf might not hurt you, the toxins are readily extracted in alcohol, so you'd be maximizing your exposure to them by making a liqueur.

Further, most of the aromatic compounds in the tomato leaves and stems are going to be very bitter anyway, so even if this weren't dangerous, it would be of dubious culinary use.

Tomato Toxicity from WikiPedia: http://en.wikipedia.org/wiki/Tomato#Plant_toxicity

Source: http://www.anaturalway.com/NightShade%20Alkaloid%20Toxins.html