droppable_accumulator breaks GCC 4.6.2 in C++11 mode

[Bryce Adelstein Lelbach]

Including Boost.Accumulators breaks for me, using GCC 4.6.2 (in C++11 mode) on the top of trunk (77425). Platform is x86-64 Linux.

In file included from /home/wash/development/boost/debug-install/boost/accumulators/framework/accumulator_set.hpp:28:0,
                 from /home/wash/development/boost/debug-install/boost/accumulators/accumulators.hpp:12,
                 from /home/wash/development/hpx_release/hpx/util/block_profiler.hpp:15,
                 from /home/wash/development/hpx_release/hpx/lcos/packaged_task.hpp:21,
                 from /home/wash/development/hpx_release/hpx/lcos/async.hpp:13,
                 from /home/wash/development/hpx_release/hpx/runtime/agas/addressing_service.hpp:30,
                 from /home/wash/development/hpx_release/hpx/runtime/naming/resolver_client.hpp:11,
                 from /home/wash/development/hpx_release/hpx/runtime.hpp:14,
                 from /home/wash/development/hpx_release/src/exception.cpp:11:
/home/wash/development/boost/debug-install/boost/accumulators/framework/accumulators/droppable_accumulator.hpp: In copy constructor ‘boost::accumulators::droppable_accumulator<Accumulator>::droppable_accumulator(const boost::accumulators::droppable_accumulator<Accumulator>&)’:
/home/wash/development/boost/debug-install/boost/accumulators/framework/accumulators/droppable_accumulator.hpp:173:54: error: expected type-specifier
/home/wash/development/boost/debug-install/boost/accumulators/framework/accumulators/droppable_accumulator.hpp:173:54: error: expected ‘>’
/home/wash/development/boost/debug-install/boost/accumulators/framework/accumulators/droppable_accumulator.hpp:173:54: error: expected ‘(’
/home/wash/development/boost/debug-install/boost/accumulators/framework/accumulators/droppable_accumulator.hpp:173:82: error: expected ‘)’ before ‘const’

[Eric Niebler]

Forgot a typename. Fixed on trunk as of [77437]. Sorry 'bout that.