Add shared subtree support, suggested by Vladimir Dronnikov. Also break out a

few new (unfinished) config options, which I intend to make hidden (but
enabled) when CONFIG_NITPICK is disabled.  Getting the .config infrastructure
to do that is non-obvious, it seems...

include/platform.h

@@ -228,6 +228,35 @@ typedef unsigned long long int  uintmax_t;
 
 #if defined(__linux__)
 #include <sys/mount.h>
+// Make sure we have all the new mount flags we actually try to use.
+#ifndef MS_BIND
+#define MS_BIND        (1<<12)
+#endif
+#ifndef MS_MOVE
+#define MS_MOVE        (1<<13)
+#endif
+#ifndef MS_RECURSIVE
+#define MS_RECURSIVE   (1<<14)
+#endif
+#ifndef MS_SILENT
+#define MS_SILENT      (1<<15)
+#endif
+
+// The shared subtree stuff, which went in around 2.6.15
+#ifndef MS_UNBINDABLE
+#define MS_UNBINDABLE  (1<<17)
+#endif
+#ifndef MS_PRIVATE
+#define MS_PRIVATE     (1<<18)
+#endif
+#ifndef MS_SLAVE
+#define MS_SLAVE       (1<<19)
+#endif
+#ifndef MS_SHARED
+#define MS_SHARED      (1<<20)
+#endif
+
+ 
 #if !defined(BLKSSZGET)
 #define BLKSSZGET _IO(0x12, 104)
 #endif