When ffsync is running, we have an error while the upgrade :
The log of install :
```bash
+ sudo make build
virtualenv --python=`which python2 python | head -n 1` --no-site-packages ./local
New python executable in ./local/bin/python2
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/virtualenv.py", line 2378, in <module>
main()
File "/usr/lib/python3/dist-packages/virtualenv.py", line 830, in main
symlink=options.symlink)
File "/usr/lib/python3/dist-packages/virtualenv.py", line 999, in create_environment
site_packages=site_packages, clear=clear, symlink=symlink))
File "/usr/lib/python3/dist-packages/virtualenv.py", line 1316, in install_python
shutil.copyfile(executable, py_executable)
File "/usr/lib/python2.7/shutil.py", line 83, in copyfile
with open(dst, 'wb') as fdst:
IOError: [Errno 26] Text file busy: './local/bin/python2'
Running virtualenv with interpreter /usr/bin/python2
Makefile:22: recipe for target 'local/COMPLETE' failed
make: *** [local/COMPLETE] Error 1
+ '[' -f /tmp/ffsync_swapfile ']'
```
