(dirname): Include ctype.h.

[IN_CTYPE_DOMAIN]: Define.
[ISALPHA]: Define.
[MSDOS]: Add support for DOS-style file names with drive letters.
Based on a patch from Eli Zaretskii.

lib/dirname.c

@@ -1,5 +1,5 @@
 /* dirname.c -- return all but the last element in a path
-   Copyright (C) 1990 Free Software Foundation, Inc.
+   Copyright (C) 1990, 1998 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -16,22 +16,31 @@
    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
 
 #ifdef HAVE_CONFIG_H
-#include <config.h>
+# include <config.h>
 #endif
 
 #ifdef STDC_HEADERS
-#include <stdlib.h>
+# include <stdlib.h>
 #else
 char *malloc ();
 #endif
-#if defined(STDC_HEADERS) || defined(HAVE_STRING_H)
-#include <string.h>
+#if defined STDC_HEADERS || defined HAVE_STRING_H
+# include <string.h>
 #else
-#include <strings.h>
-#ifndef strrchr
-#define strrchr rindex
+# include <strings.h>
+# ifndef strrchr
+#  define strrchr rindex
+# endif
 #endif
+
+#include <ctype.h>
+
+#if defined STDC_HEADERS || (!defined isascii && !defined HAVE_ISASCII)
+# define IN_CTYPE_DOMAIN(c) 1
+#else
+# define IN_CTYPE_DOMAIN(c) isascii(c)
 #endif
+#define ISALPHA(Ch) (IN_CTYPE_DOMAIN (Ch) && isalpha (Ch))
 
 /* Return the leading directories part of PATH,
    allocated with malloc.  If out of memory, return 0.
@@ -55,6 +64,13 @@ dirname (path)
     }
   else
     {
+      char *lim = path;
+
+#ifdef MSDOS
+      /* If canonicalized "d:/path", leave alone the root case "d:/".  */
+      lim = (ISALPHA (path[0]) && path[1] == ':') ? path + 2 : path;
+#endif
+
       /* Remove any trailing slashes from the result.  */
       while (slash > path && *slash == '/')
 	--slash;