Support backup and restore of special files on POSIX style systems

Special files are device nodes and named pipes. The necessity of the
former is clear, the latter is debatable.
In order to preserve backward compatibility, the device number is
encoded in the StartChunk/StartOffset fields of the entry.

src/duplicacy_backupmanager.go

@@ -797,6 +797,21 @@ func (manager *BackupManager) Restore(top string, revision int, inPlace bool, qu
 			}
 			remoteEntry.RestoreEarlyDirFlags(fullPath)
 			directoryEntries = append(directoryEntries, remoteEntry)
+		} else if remoteEntry.IsSpecial() {
+			if stat, _ := os.Lstat(fullPath); stat != nil {
+				if !overwrite {
+					LOG_WERROR(allowFailures, "DOWNLOAD_OVERWRITE",
+						"File %s already exists.  Please specify the -overwrite option to overwrite", remoteEntry.Path)
+					continue
+				}
+				os.Remove(fullPath)
+			}
+
+			if err := remoteEntry.RestoreSpecial(fullPath); err != nil {
+				LOG_ERROR("RESTORE_SPECIAL", "Unable to restore special file %s: %v", remoteEntry.Path, err)
+				return 0
+			}
+			remoteEntry.RestoreMetadata(fullPath, nil, setOwner)
 		} else {
 			if remoteEntry.IsHardlinkRoot() {
 				hardLinkTable[len(hardLinkTable)-1] = hardLinkEntry{remoteEntry, true}