bug#8093: etags: Downcase drive letters, for consistency with Emacs proper.

[Paul Eggert]

Emacs downcases drive letters when canonicalizing file names on
Microsoft Windows, but etags upcases them.  etags should be consistent
with Emacs.  I found this problem by code inspection, because there's
a macro 'upcase' that normally isn't used in etags.c; its only use is
in the section of code that upcases drive letters.  Here's a proposed
patch.

2011-02-21  Paul Eggert  <eggert@cs.ucla.edu>

        etags: Downcase drive letters, for consistency with Emacs proper.
        * etags.c (upcase): Remove; no longer used.
        (canonicalize_filename): Downcase drive letters.

--- lib-src/etags.c     2011-02-21 16:47:08.883947000 -0800
+++ /u/cs/fac/eggert/junk/etags.c       2011-02-21 21:21:04.074974000 -0800
@@ -239,7 +239,6 @@ If you want regular expression support,
 #define ISLOWER(c)     islower (CHAR(c))
 
 #define lowcase(c)	tolower (CHAR(c))
-#define upcase(c)      toupper (CHAR(c))
 
 
 /*
@@ -6638,7 +6637,7 @@ filename_is_absolute (char *fn)
          );
 }
 
-/* Upcase DOS drive letter and collapse separators into single slashes.
+/* Downcase DOS drive letter and collapse separators into single slashes.
    Works in place. */
 static void
 canonicalize_filename (register char *fn)
@@ -6648,8 +6647,8 @@ canonicalize_filename (register char *fn
 
 #ifdef DOS_NT
   /* Canonicalize drive letter case.  */
-  if (fn[0] != '\0' && fn[1] == ':' && ISLOWER (fn[0]))
-    fn[0] = upcase (fn[0]);
+  if (fn[0] != '\0' && fn[1] == ':' && ISUPPER (fn[0]))
+    fn[0] = downcase (fn[0]);
 
   sep = '\\';
 #endif