Prevent cyclic imports

[alarbada]

Cyclic imports add an infinite loop in the latest jet version.

Edit:

This:

<!-- file test1.html -->
{{ import "./test2.html" }}
<p> hi </p>

<!-- file test2.html -->
{{ import "./test1.html" }}
<p> hello </p>

Makes jet go into an infinite loop when executing one of these templates.