pyhesiodfs should know how to fallback to lower-priority lockers

[geofft]

# FIXME check if the first locker is valid
if len(filsys.filsys) >= 1:
    pointers = filsys.filsys
    pointer = pointers[0]

[geofft]

One issue is that open() and the like can block indefinitely if AFS is down. So we should spawn a new thread to open or stat the directory, and fall back if the thread does not terminate within a second or two.

But I have some concerns about that:

• Can we terminate the thread, if it ends up unkillably in kernel space? Is it fine to leak these threads until AFS resolves itself?
• Can threading with Python not suck?
• Can threading with FUSE not suck?

[xavid]

I would hope that CPython releases the GIL before calling open(). If my optimism is merited, Python threading won't be a problem here.

I've used threading with the C fuse interface before and didn't need to do anything terribly weird.