1. Modify some fuse class method so that it can work with cffi.
for example path = ffi.string(path)
since the c library will path a <cdata char*> to python level,
we need to use ffi.string to trasfer it into python string.
2. Found out that in fuse.__init__, the fuse_ops registration process may cause some problem,
seems like if we use the same variable name, the whole process will be messed up.