## Changes
This PR removes the stat call and instead relies on errors returned by
the go SDK to return the appropriate errors
## Tests
Tested using existing filer integration tests
## Changes
Local file reads on Windows require the file handle to be closed after
using it. This commit includes an interface change to return an
`io.ReadCloser` from `Read` to accommodate this.
## Tests
The existing integration tests for the filer interface all pass.
## Changes
This PR:
1. Adds the export-dir command
2. Changes filer.Read to return an error if a user tries to read a
directory
3. Adds returning internal file structures from filer.Stat().Sys()
## Tests
Integration tests and manually
## Changes
This captures the recursive deletion of a directory tree in the filer interface.
Prompted by #433.
## Tests
Integration tests pass (ran the filer ones on AWS and Azure).
Adds a DBFS implementation of the `filer.Filer` interface.
The integration tests are reused between the workspace filesystem and
DBFS implementations to ensure identical behavior.
shreyas-goenka
Pieter Noordhuis