functional (bind): Remove from overload set when first argument type might be a socket file descriptor.

2011-05-03  Jonathan Wakely  <jwakely.gcc@gmail.com>

	* include/std/functional (bind): Remove from overload set when first
	argument type might be a socket file descriptor.
	* testsuite/20_util/bind/socket.cc: New.

From-SVN: r173279