Archaic or poetic English
As Webster tells us (albeit in flowery language) "wert" is an obsolete or deprecated form of "were" or "wart". Nowadays, about the only time you will see it is in poetry, and I can think of nothing which illustrates its usage better than this:
Ode to a Skylark by Percy Bysshe Shelley
Hail to thee, blithe spirit!
Bird thou never wert --
That from heaven or near it
Pourest thy full heart
In profuse strains of unpremeditated art
Oh,and furthermore, it's nothing to do with my username...
Well, evilrooster challenged me to do it...