Fixing bug 502723 - updater checks the wrong MAX_PATH define.

Patch my Mook <mook@songbirdnest.com>.
r=robstrong.

toolkit/mozapps/update/src/updater/updater.cpp

@@ -120,7 +120,7 @@ void LaunchChild(int argc, char **argv);
 #ifndef MAXPATHLEN
 # ifdef PATH_MAX
 #  define MAXPATHLEN PATH_MAX
-# elif defined(_MAX_PATH)
+# elif defined(MAX_PATH)
 #  define MAXPATHLEN MAX_PATH
 # elif defined(_MAX_PATH)
 #  define MAXPATHLEN _MAX_PATH