Fix indent guide

This fixes the indent guide when lines around the whitespace lines change. It will check whitespace lines surrounding a change. If their indent level changes, it will invalidate the whitespace lines.

Fixes this issue:

![ba4df5ea-f898-11e3-9fcd-686fe9e0ea2c](https://cloud.githubusercontent.com/assets/69169/3378927/0bd7fa88-fbea-11e3-8427-0256ec8fa576.png)

@nathansobo will you check the changes in tokenized-buffer and make sure it's legit? Also, let me know if there are benchmarks I can run to make sure typing is ok.

ref #2367
"updates the indentLevel of empty lines that follow the change"

The fact that the only way to test this right now is at the end of the buffer seems less important than consistency between the description strings for the before/after cases.