Test: set_text is triggered exactly once after save

Hi, I've noticed that set_text is triggered twice after node name edit, and then blur (and possibly three times if this condition is met https://github.com/vakata/jstree/blob/e2923e840d47eef45358ea9236c2cb6b15bf6e41/dist/jstree.js#L4061).

I cannot offer a solution at the moment, because event triggering is not well separated from associated functions, and some more rewrites would be required, or maybe that's the point, triggering events every time, but anyway I wrote a test to prove this bug.

I see tests has been just started for this project, so this might not be the right way of writing tests for jstree, so please feel free to not merge this pull request and just treat is as a bug report.

(With this test come another bug: jstree instance cannot be destroyed right after initialization because of this timeout: https://github.com/vakata/jstree/blob/e2923e840d47eef45358ea9236c2cb6b15bf6e41/dist/jstree.js#L711, so it would be nice to have tests started anyway,)