Enable StatFS on dynamicfs

MacOS apparently invokes StatFS on os.Lstat/os.Stat. Note that the
return fields are not actually populated here.

samples/dynamicfs/dynamic_fs.go

@@ -1,20 +1,20 @@
 package dynamicfs
 
 import (
-	"strings"
+	"fmt"
 	"io"
+	"log"
+	"os"
+	"strings"
+	"sync"
+	"time"
 
 	"golang.org/x/net/context"
 
-	"github.com/jacobsa/timeutil"
 	"github.com/jacobsa/fuse"
-	"github.com/jacobsa/fuse/fuseutil"
 	"github.com/jacobsa/fuse/fuseops"
-	"os"
-	"fmt"
-	"log"
-	"sync"
-	"time"
+	"github.com/jacobsa/fuse/fuseutil"
+	"github.com/jacobsa/timeutil"
 )
 
 // Create a file system that contains 2 files (`age` and `weekday`) and no directories. Every time
@@ -131,7 +131,6 @@ func (fs *dynamicFS) findUnusedHandle() fuseops.HandleID {
 		handle++
 	}
 	fs.nextHandle = handle + 1
-	log.Printf("Minting new handle: %d", handle)
 	return handle
 }
 
@@ -275,3 +274,8 @@ func (fs *dynamicFS) ReleaseFileHandle(
 	delete(fs.fileHandles, op.Handle)
 	return
 }
+
+func (fs *dynamicFS) StatFS(ctx context.Context,
+	op *fuseops.StatFSOp) (err error) {
+	return
+}