Fixes #14 Properly checks dimensional lengths using ndim.

Auxiliary coordinate variables are also allowed, so the dim==name portion has been removed.  Reformatted check to properly check for the increase in dimensionality.
Also, if you can avoid putting content into both the then/else blocks, you can make code a bit more readable:

```python
valid = True
if ndim != otherndim + 1:
    valid = False
    reasoning = "blabla"
```