Bugfixes and performance improvements

This pull request addresses a few reported issues, and updates libfte and emscripten to their latest versions. Specifically:

* Issue #25: uTransformers bails when ```max_*_len``` is large
* Issue #27: uTransformers.rabbit segfaults on ```set_key```
* Issue #28: update libfte and emscripten to the latest versions

This pull request results in substantial performance improvements for uTransformers. Performance for ```.*``` languages is now approaching that of using uTransformers.rabbit. (See attached image.) 

![screen shot 2014-07-13 at 4 02 11 pm](https://cloud.githubusercontent.com/assets/2654449/3566055/785c482e-0ae2-11e4-914c-5ec491eea19e.png)