Add 'extra_style_parser' method to basic_command_line_parser. Previously

this functionality was not available to use user due to private
derivation from detail::cmdline.


[SVN r31491]

libs/program_options

@@ -1 +1 @@
-Subproject commit a00a6c9d1925f1dd9e0a18f92ecec3f202eaf99c
+Subproject commit e7e1550269eb5bdb6a9b736897daab654d6f5d59