Add support for flock()

[nnseva]

Implementing the flock operation is not available, while probably required for a network filesystem, or just a filesystem supporting consistent concurrent file access.

The original libfuse library supports flock operation. Please implement a hook redirecting flock operation to the python code.

[ThomasWaldmann]

See the front page about "no longer developed".

In case you can develop it and someone can review it, don't let that hold you back!