Fix zfs "redact" misc issues

* zfs redact error messages do not end with newline character
 * 30af21b0 inadvertently removed some ZFS_PROP comments
 * man/zfs: zfs redact <redaction_snapshot> is not optional

Reviewed-by: Giuseppe Di Natale <guss80@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #8988

include/sys/fs/zfs.h

@@ -118,11 +118,11 @@ typedef enum {
 	ZFS_PROP_PRIVATE,		/* not exposed to user, temporary */
 	ZFS_PROP_ACLINHERIT,
 	ZFS_PROP_CREATETXG,
-	ZFS_PROP_NAME,
+	ZFS_PROP_NAME,			/* not exposed to the user */
 	ZFS_PROP_CANMOUNT,
-	ZFS_PROP_ISCSIOPTIONS,
+	ZFS_PROP_ISCSIOPTIONS,		/* not exposed to the user */
 	ZFS_PROP_XATTR,
-	ZFS_PROP_NUMCLONES,
+	ZFS_PROP_NUMCLONES,		/* not exposed to the user */
 	ZFS_PROP_COPIES,
 	ZFS_PROP_VERSION,
 	ZFS_PROP_UTF8ONLY,
@@ -140,12 +140,12 @@ typedef enum {
 	ZFS_PROP_USEDDS,
 	ZFS_PROP_USEDCHILD,
 	ZFS_PROP_USEDREFRESERV,
-	ZFS_PROP_USERACCOUNTING,
-	ZFS_PROP_STMF_SHAREINFO,
+	ZFS_PROP_USERACCOUNTING,	/* not exposed to the user */
+	ZFS_PROP_STMF_SHAREINFO,	/* not exposed to the user */
 	ZFS_PROP_DEFER_DESTROY,
 	ZFS_PROP_USERREFS,
 	ZFS_PROP_LOGBIAS,
-	ZFS_PROP_UNIQUE,
+	ZFS_PROP_UNIQUE,		/* not exposed to the user */
 	ZFS_PROP_OBJSETID,
 	ZFS_PROP_DEDUP,
 	ZFS_PROP_MLSLABEL,
@@ -156,7 +156,7 @@ typedef enum {
 	ZFS_PROP_CLONES,
 	ZFS_PROP_LOGICALUSED,
 	ZFS_PROP_LOGICALREFERENCED,
-	ZFS_PROP_INCONSISTENT,
+	ZFS_PROP_INCONSISTENT,		/* not exposed to the user */
 	ZFS_PROP_VOLMODE,
 	ZFS_PROP_FILESYSTEM_LIMIT,
 	ZFS_PROP_SNAPSHOT_LIMIT,