example/fcgi/server4: Add missing namespace qualifier

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
fcgi::*: Fix layering violations

Several places attempted to get at socket_ (which is private for me),
use next_layer() instead.

async_accept() was calling an unimplemented io_service(), i assume this
is meant to be get_io_service().

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
fcgi::* Fix some layering violations

Not sure about that one; Does it take a connection pointer ?
Did not see a testcase in the examples that would exercise this one,
so just guess..

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
Fixup constness of async_read_some() incoming buffer

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>