EINTR is commonly encountered when running under a debugger, so this
change makes it possible to do so without hitting spurious
EINTR errors.

Fixes #39.

This makes automated import rewriting more robust.

The code confuses the race-detector, and the work-arounds to fool the
race-detector fools humans. No conclusive benchmark data supports
the usefulness of the handle maps.

This is necessary to work around apparent bugs in the OSX FUSE
implementation.

OSXFUSE requires STATFS to always be present.

This protects against deadlock should the kernel issue a lookup
synchronously in response. This behavior has been seen on Linux
3.15.3-200.fc20.x86_64.