viewer.setMouseUsage('rotate') does not work with md2.html

```
What steps will reproduce the problem?
1. using the md2viwer.html
2. put in the controls from the test.html page
3.

What is the expected output? What do you see instead?
I thought it would allow me to control the zoom and rotate separately. instead
it still only rotates and zooms if i hold down shift. I also get the error
that viewer.setMouseUsage('rotate') is not defined

What version of the product are you using? On what operating system?
im using jsc3d-full-0.9.8. im using it on macOSX 10.6.8 and also on the ipad2.

Please provide any additional information below.
I wanted to use the separate controls since on the ipad it only rotates without
the option of zoom unless your using the controls on test.html page. it works
with the other stationary models but not with the md2 model
```

Original issue reported on code.google.com by `c...@zimfly.com` on 23 May 2013 at 4:06

Start by comparing the controls in md2viewer.html with those in test.html, then inspect where viewer.setMouseUsage('rotate') is exposed or called. Reproduce the issue with the md2 model and check why the method is undefined there. Done means rotation and zoom can be controlled separately without holding Shift, including on the iPad.

Written by the indexing model from the issue text.