Change strand implementation so that dispatch will execute a handler

immediately if called from within the strand.

Add hook function for customising handler dispatch.

Need to use reinterpret_cast when testing for enable_connection_aborted
socket option, to allow non-int socket options to compile correctly.


[SVN r34464]

libs/asio

@@ -1 +1 @@
-Subproject commit 8075fa5a446927b4cdbf2e8131ea4c1114b1ab8b
+Subproject commit 7027bf39d5b50c987fb232070968b251ce9137b6