Mark translatable string with `N_ (...)'.

src/df.c

@@ -43,7 +43,7 @@
 #define PROGRAM_NAME "df"
 
 #define AUTHORS \
-  "Torbjorn Granlund, David MacKenzie, Larry McVoy, and Paul Eggert"
+  N_ ("Torbjorn Granlund, David MacKenzie, Larry McVoy, and Paul Eggert")
 
 char *xgetcwd ();
 

src/du.c

@@ -63,7 +63,7 @@
 #define PROGRAM_NAME "du"
 
 #define AUTHORS \
-  "Torbjorn Granlund, David MacKenzie, Larry McVoy, and Paul Eggert"
+  N_ ("Torbjorn Granlund, David MacKenzie, Larry McVoy, and Paul Eggert")
 
 /* Initial size of the hash table.  */
 #define INITIAL_TABLE_SIZE 103

src/tail.c

@@ -46,7 +46,7 @@
 #define PROGRAM_NAME "tail"
 
 #define AUTHORS \
-  "Paul Rubin, David MacKenzie, Ian Lance Taylor, and Jim Meyering"
+  N_ ("Paul Rubin, David MacKenzie, Ian Lance Taylor, and Jim Meyering")
 
 #ifndef ENOSYS
   /* Some systems don't have ENOSYS -- this should be a big enough

src/touch.c

@@ -36,7 +36,7 @@
 #define PROGRAM_NAME "touch"
 
 #define AUTHORS \
-  "Paul Rubin, Arnold Robbins, Jim Kingdon, David MacKenzie, and Randy Smith"
+N_ ("Paul Rubin, Arnold Robbins, Jim Kingdon, David MacKenzie, and Randy Smith")
 
 #ifndef STDC_HEADERS
 time_t time ();