PelicanFS unclosed client connection warnings

[turetske]

PelicanFS when used with Rasterio seems to generate a lot of unclosed client connections. It also is very slow. The reason for this is unclear and why it's solely with Rasterio.

Potentially an issue with glob/walk?

Investigate and figure out the solution.

[duncanmmacleod]

@turetske this may be resolved by #141, but I haven't checked closely. I also have no idea what Rasterio is.