Improve 'bool_switch' -- don't accept any argument on the command line.

Allow to set 'zero_tokens' flag for the typed_value type.


[SVN r25105]

libs/program_options

@@ -1 +1 @@
-Subproject commit 7fa6a814ab2f7c3c0210b58baed4f2a2bbfeee1e
+Subproject commit 44d5ba98c10921bb7e98494d1ec77586ee6e5518