chunker: implementation + required fstest patch

Note: chunker implements many irrelevant methods (UserInfo, Disconnect etc),
but they are required by TestIntegration/FsCheckWrap and cannot be removed.

Dropped API methods: MergeDirs DirCacheFlush PublicLink UserInfo Disconnect OpenWriterAt

Meta formats:
- renamed old simplejson format to wdmrcompat.
- new simplejson format supports hash sums and verification of chunk size/count.

Change list:
- split-chunking overlay for mailru
- add to all
- fix linter errors
- fix integration tests
- support chunks without meta object
- fix package paths
- propagate context
- fix formatting
- implement new required wrapper interfaces
- also test large file uploads
- simplify options
- user friendly name pattern
- set default chunk size 2G
- fix building with golang 1.9
- fix ci/cd on a separate branch
- fix updated object name (SyncUTFNorm failed)
- fix panic in Box overlay
- workaround: Box rename failed if name taken
- enhance comments in unit test
- fix formatting
- embed wrapped remote rather than inherit
- require wrapped remote to support move (or copy)
- implement 3 (keep fstest)
- drop irrelevant file system interfaces
- factor out Object.mainChunk
- refactor TestLargeUpload as InternalTest
- add unit test for chunk name formats
- new improved simplejson meta format
- tricky case in test FsIsFile (fix+ignore)
- remove debugging print
- hide temporary objects from listings
- fix bugs in chunking reader:
  - return EOF immediately when all data is sent
  - handle case when wrapped remote puts by hash (bug detected by TestRcat)
- chunked file hashing (feature)
- server-side copy across configs (feature)
- robust cleanup of temporary chunks in Put
- linear download strategy (no read-ahead, feature)
- fix unexpected EOF in the box multipart uploader
- throw error if destination ignores data

backend/chunker/chunker_test.go

@@ -0,0 +1,54 @@
+// Test the Chunker filesystem interface
+package chunker_test
+
+import (
+	"flag"
+	"os"
+	"path/filepath"
+	"testing"
+
+	_ "github.com/rclone/rclone/backend/all" // for integration tests
+	"github.com/rclone/rclone/backend/chunker"
+	"github.com/rclone/rclone/fstest"
+	"github.com/rclone/rclone/fstest/fstests"
+)
+
+// Command line flags
+var (
+	// Invalid characters are not supported by some remotes, eg. Mailru.
+	// We enable testing with invalid characters when -remote is not set, so
+	// chunker overlays a local directory, but invalid characters are disabled
+	// by default when -remote is set, eg. when test_all runs backend tests.
+	// You can still test with invalid characters using the below flag.
+	UseBadChars = flag.Bool("bad-chars", false, "Set to test bad characters in file names when -remote is set")
+)
+
+// TestIntegration runs integration tests against a concrete remote
+// set by the -remote flag. If the flag is not set, it creates a
+// dynamic chunker overlay wrapping a local temporary directory.
+func TestIntegration(t *testing.T) {
+	opt := fstests.Opt{
+		RemoteName:                   *fstest.RemoteName,
+		NilObject:                    (*chunker.Object)(nil),
+		SkipBadWindowsCharacters:     !*UseBadChars,
+		UnimplementableObjectMethods: []string{"MimeType"},
+		UnimplementableFsMethods: []string{
+			"PublicLink",
+			"OpenWriterAt",
+			"MergeDirs",
+			"DirCacheFlush",
+			"UserInfo",
+			"Disconnect",
+		},
+	}
+	if *fstest.RemoteName == "" {
+		name := "TestChunker"
+		opt.RemoteName = name + ":"
+		tempDir := filepath.Join(os.TempDir(), "rclone-chunker-test-standard")
+		opt.ExtraConfig = []fstests.ExtraConfigItem{
+			{Name: name, Key: "type", Value: "chunker"},
+			{Name: name, Key: "remote", Value: tempDir},
+		}
+	}
+	fstests.Run(t, &opt)
+}