## 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).
## Changes
The pattern `errors.Is(err, fs.ErrNotExist)` is common to check for an
error type.
Errors can implement `Is(error) bool` with a custom equivalence checker.
## Tests
New asserts all pass in the integration test.
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.
Pieter Noordhuis
shreyas-goenka