Changed "\," to "\cdot " for LaTeX #351

To make LaTeX export display centered dot instead of space for multiplication.

**This should be reviewed and tested before merging!** I am not sure if "m_hidden" is used for anything more than just multiplication, so there might be issues!

The small space now used for multiplication can be confusing as seen in the pictures.
![no_cdot](https://cloud.githubusercontent.com/assets/9117693/4951681/4cf0690c-666a-11e4-9a8d-1a3a78fb64e7.png)
![cdot](https://cloud.githubusercontent.com/assets/9117693/4951682/505210fa-666a-11e4-9c8f-9e8b1012e368.png)