Fix import bug in pycpufit

The import statement in `Cpufit/python/pycpufit/__init__.py` causes this
error:

```
Traceback (most recent call last):
  File "Gpufit/build/pyCpufit/setup.py", line 10, in <module>
    import pycpufit.version as vs
  File "Gpufit/build/pyCpufit/pycpufit/__init__.py", line 1, in <module>
    from cpufit import *
```

This commit makes the import fully qualififed, which fixes the problem.

Cpufit/python/pycpufit/__init__.py

@@ -1 +1 @@
-from cpufit import *
+from pycpufit.cpufit import *