Fix the use of struct utmp/utmpx in comsatd.

* am/utmp.m4: Check if struct utmp has ut_user or ut_name members.
* comsat/comsat.c [HAVE_UTMPX_H]: Define UTMP as a typedef of
struct utmpx.
Define ut_user, if necessary.
(find_user): Use ut_user instead of (backward-compatible) ut_name.

@@ -2,7 +2,7 @@ dnl MU_CHECK_UTMP -- Check for the presence of utmp.h, setutent, getutent
 dnl                  and endutent calls.
 AC_DEFUN([MU_CHECK_UTMP],
 [
-  AC_CHECK_HEADERS([utmp.h])
+  AC_CHECK_HEADERS([utmp.h utmpx.h])
   # The three functions setutent,getutent and endutent depend on each other,
   # so it seems reasonable to provide replacements for all three if getutent
   # is not present.
@@ -11,4 +11,10 @@ AC_DEFUN([MU_CHECK_UTMP],
          [Define if your system has the three ???utent functions]),
                  [if test "$ac_cv_header_utmp_h" = "yes"; then
 		   AC_LIBOBJ([utmp])
-		 fi])])
+		 fi])
+  if test "$ac_cv_header_utmp_h" = "yes"; then
+    AC_CHECK_MEMBERS([struct utmp.ut_user, struct utmp.ut_name],,,
+                     [#include <sys/types.h>
+#include <utmp.h>])
+  fi
+])

@@ -36,10 +36,8 @@ extern void setutent (void);
 extern struct utmp *getutent (void);
 #endif
 
-#ifdef UTMPX
-# ifdef HAVE_UTMPX_H
+#ifdef HAVE_UTMPX_H
 # include <utmpx.h>
-# endif
 typedef struct utmpx UTMP;
 # define SETUTENT() setutxent()
 # define GETUTENT() getutxent()
@@ -49,6 +47,13 @@ typedef struct utmp UTMP;
 # define SETUTENT() setutent()
 # define GETUTENT() getutent()
 # define ENDUTENT() endutent()
+# if !HAVE_STRUCT_UTMP_UT_USER
+#  if HAVE_STRUCT_UTMP_UT_NAME
+#   define ut_user ut_name
+#  else
+#   error "Neither ut_user nor ut_name found in struct utmp. Please report."
+#  endif
+# endif
 #endif
 
 #define MAX_TTY_SIZE (sizeof (PATH_TTY_PFX) + sizeof (((UTMP*)0)->ut_line))
@@ -462,7 +467,7 @@ find_user (const char *name, char *tty)
       if (uptr->ut_type != USER_PROCESS)
 	continue;
 #endif
-      if (!strncmp (uptr->ut_name, name, sizeof(uptr->ut_name)))
+      if (!strncmp (uptr->ut_user, name, sizeof(uptr->ut_user)))
 	{
 	  /* no particular tty was requested */
 	  strncpy (ftty + sizeof(PATH_DEV),