Set CREATE_NO_WINDOW in tor_spawn_background.

This flag prevents the creation of a console window popup on Windows. We
need it for pluggable transport executables--otherwise you get blank
console windows when you launch the 3.x browser bundle with transports
enabled.

http://msdn.microsoft.com/en-us/library/ms684863.aspx#CREATE_NO_WINDOW

The browser bundles that used Vidalia used to set this flag when
launching tor itself; it was apparently inherited by the pluggable
transports launched by tor. In the 3.x bundles, tor is launched by some
JavaScript code, which doesn't have the ability to set CREATE_NO_WINDOW.
tor itself is now being compiled with the -mwindows option, so that it
is a GUI application, not a console application, and doesn't show a
console window in any case. This workaround doesn't work for pluggable
transports, because they need to be able to write control messages to
stdout.

https://trac.torproject.org/projects/tor/ticket/9444#comment:30

changes/bug10297

@@ -0,0 +1,4 @@
+  o Minor features:
+    - Spawn background processes using the CREATE_NO_WINDOW flag on
+      Windows, in order to prevent a console window from appearing.
+      Resolves ticket 10297.

src/common/util.c

@@ -3803,7 +3803,7 @@ tor_spawn_background(const char *const filename, const char **argv,
                  TRUE,          // handles are inherited
   /*(TODO: set CREATE_NEW CONSOLE/PROCESS_GROUP to make GetExitCodeProcess()
    * work?) */
-                 0,             // creation flags
+                 CREATE_NO_WINDOW,             // creation flags
                  (env==NULL) ? NULL : env->windows_environment_block,
                  NULL,          // use parent's current directory
                  &siStartInfo,  // STARTUPINFO pointer