Use the default provided to RangeParameter

The "default" parameter to RangeParameter is ignored, resulting in the following error if the default is specified:

```
2013-02-02 22:57:37,932 - ERROR - Unable to load model from 'splits'
Traceback (most recent call last):
  File "/var/npsgd/npsgd/model_manager.py", line 118, in setupModels
    module = imp.load_source(importName, pyfile)
  File "/var/npsgd_models/spec/splits.py", line 17, in <module>
    class SPLITS(StandaloneTask):
  File "/var/npsgd_models/spec/splits.py", line 25, in SPLITS
    default=(400,700), rangeStart=310, rangeEnd=1000, step=5, units="nm", helpText="Modeled spectral curves will be generated in steps of 5nm."),
  File "/var/npsgd/npsgd/model_parameters.py", line 261, in __init__
    self.setValue(self.default)
  File "/var/npsgd/npsgd/model_parameters.py", line 267, in setValue
    start, end = map(float, value)
TypeError: argument 2 to map() must support iteration
```