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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.

Tony's changes to error handling in the CUDA platform so it throws exceptions instead of calling exit()

Moved SFMT into libraries folder, and restructured it to allow multiple independent random number generators

Added #include <cstdlib> to header files so would work with gcc 4.4.2.  Also changed includes of stdlib.h and string.h to cstdlib.h and cstring.h

Changed format from %u to %zu for size_t entries

Removed routines to copy forces: Peter pointed out a shallow copy using copy constructors is sufficient