Fix putenv and unsetenv on MS-Windows.

src/w32.c (unsetenv): Return 0 if the input string is too long.

 nt/inc/ms-w32.h (sys_putenv): Add prototype.

Fixes: debbugs:13070

nt/ChangeLog

@@ -1,6 +1,7 @@
 2012-12-08  Eli Zaretskii  <eliz@gnu.org>
 
 	* inc/ms-w32.h (putenv): Redirect to sys_putenv.
+	(sys_putenv): Add prototype.
 
 	* config.nt (HAVE_UNSETENV): Define to 1.
 

nt/inc/ms-w32.h

@@ -381,6 +381,7 @@ extern char *get_emacs_configuration_options (void);
 # undef putenv
 #endif
 #define putenv    sys_putenv
+extern int sys_putenv (char *);
 
 extern int getloadavg (double *, int);
 extern int getpagesize (void);

src/ChangeLog

@@ -1,3 +1,7 @@
+2012-12-08  Eli Zaretskii  <eliz@gnu.org>
+
+	* w32.c (unsetenv): Return 0 if the input string is too long.
+
 2012-12-08  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Use putenv+unsetenv instead of modifying environ directly (Bug#13070).

src/w32.c

@@ -1562,7 +1562,7 @@ unsetenv (const char *name)
   if (name_len > 32767)
     {
       errno = ENOMEM;
-      return -1;
+      return 0;
     }
   /* It is safe to use 'alloca' with 32K size, since the stack is at
      least 2MB, and we set it to 8MB in the link command line.  */