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* Explicitly initialize Python thread support. Previously, calling
llfuse.main() resulted in a crash if no Python threads were used
before the call.
* Removed handle_exc() method. If request handle raise an exception,
the main loop now terminates and the exception is re-raised and
passed to the caller of llfuse.main().
* llfuse.close() can now leave the mountpoint in an inaccessible
state to signal a shutdown due to an internal file system
error.
* The destroy() request handler is now called without the
global lock acquired. This makes sense, because it's not called
as part of the main loop but by llfuse.close().