Win32: fix environment memory leaks

All functions that modify the environment have memory leaks.

Disable gitunsetenv in the Makefile and use env_setenv (via mingw_putenv)
instead (this frees removed environment entries).

Move xstrdup from env_setenv to make_augmented_environ, so that
mingw_putenv no longer copies the environment entries (according to POSIX
[1], "the string [...] shall become part of the environment"). This also
fixes the memory leak in gitsetenv, which expects a POSIX compliant putenv.

[1] http://pubs.opengroup.org/onlinepubs/009695399/functions/putenv.html

Note: This patch depends on taking control of char **environ and having
our own mingw_putenv (both introduced in "Win32: Unicode environment
(incoming)").

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Stepan Kasal <kasal@ucw.cz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -1220,14 +1220,14 @@ static char **env_setenv(char **env, const char *name)
 			for (i = 0; env[i]; i++)
 				;
 			env = xrealloc(env, (i+2)*sizeof(*env));
-			env[i] = xstrdup(name);
+			env[i] = (char*) name;
 			env[i+1] = NULL;
 		}
 	}
 	else {
 		free(env[i]);
 		if (*eq)
-			env[i] = xstrdup(name);
+			env[i] = (char*) name;
 		else
 			for (; env[i]; i++)
 				env[i] = env[i+1];
@@ -1242,8 +1242,10 @@ char **make_augmented_environ(const char *const *vars)
 {
 	char **env = copy_environ();
 
-	while (*vars)
-		env = env_setenv(env, *vars++);
+	while (*vars) {
+		const char *v = *vars++;
+		env = env_setenv(env, strchr(v, '=') ? xstrdup(v) : v);
+	}
 	return env;
 }
 

compat/mingw.h

@@ -209,6 +209,7 @@ char *mingw_getenv(const char *name);
 #define getenv mingw_getenv
 int mingw_putenv(const char *namevalue);
 #define putenv mingw_putenv
+#define unsetenv mingw_putenv
 
 int mingw_gethostname(char *host, int namelen);
 #define gethostname mingw_gethostname

config.mak.uname

@@ -326,7 +326,6 @@ ifeq ($(uname_S),Windows)
 	NO_IPV6 = YesPlease
 	NO_UNIX_SOCKETS = YesPlease
 	NO_SETENV = YesPlease
-	NO_UNSETENV = YesPlease
 	NO_STRCASESTR = YesPlease
 	NO_STRLCPY = YesPlease
 	NO_MEMMEM = YesPlease
@@ -479,7 +478,6 @@ ifneq (,$(findstring MINGW,$(uname_S)))
 	NO_SYMLINK_HEAD = YesPlease
 	NO_UNIX_SOCKETS = YesPlease
 	NO_SETENV = YesPlease
-	NO_UNSETENV = YesPlease
 	NO_STRCASESTR = YesPlease
 	NO_STRLCPY = YesPlease
 	NO_MEMMEM = YesPlease