More intuative error messaging

[KieranP]

In vboxweb_rb, there is a settings update form. If a wrong value is passed in, I get:

Expected an Integer parameter

However, it doesn't say which value is incorrect.

Ideally, you could make

accelerate_3d_enabled Expected an Integer parameter, but got a String "true"

If adding the params type and value is too much, simply catching the error from the com interface and prepending the field name would be helpful.

accelerate_3d_enabled Expected an Integer parameter