Git version parsing fails if 4th version number contains a string

If i execute `git --version` i get an output like `git version 1.7.12.4 (Apple Git-37)`.
If i try to run CVSAnaly2 with this git version i get the following error:

```
arsing log for CVSAnalY (git)
Exception in thread Thread-1:
Traceback (most recent call last):
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 552, in __bootstrap_inner
    self.run()
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 505, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/Users/andygrunwald/Development/CVSAnalY/pycvsanaly2/Log.py", line 62, in _logreader
    repo.log (self.uri or repo.get_uri ())
  File "/Users/andygrunwald/Development/RepositoryHandler/repositoryhandler/backends/git.py", line 264, in log
    major, minor, micro, extra = self._get_git_version()
  File "/Users/andygrunwald/Development/RepositoryHandler/repositoryhandler/backends/git.py", line 107, in _get_git_version
    self.git_version = tuple([int(i) for i in version.split('.')])
ValueError: invalid literal for int() with base 10: '4 (Apple Git-37)\n'

Executing extensions
```

With this code change the method `_get_git_version` will return `(1, 7, 12, 4)`.
The string will be cutted.