SimTk/openmm — pull request #485 by chrisdembia (2014-06-16 23:19:04+00:00)
Title: Fix Clang warning about unhandled enum values.

Clang had been generating the following warning:

```
ParsedExpression.cpp:123:13:
warning:
30 enumeration values not handled in switch: 'CONSTANT', 'VARIABLE',
'CUSTOM'...
[-Wswitch]
switch (node.getOperation().getId()) {
^
1 warning generated.
```

To get rid of this warning, I added a default case, which does nothing.