boost::lockfree:spsc_queue::consume_all returns bool instead of the number of elements consumed

[Ephraim Ofir <ephraimofir@…>]

When using the compile_time_sized_ringbuffer version of spsc_queue::consume_all, the value returned is a bool (similar to the way consume_one works) instead of the number of elements consumed (similar to the way the runtime_sized_ringbuffer version works).

This also generates the following warning in VS2012:

boost/lockfree/spsc_queue.hpp(473): warning C4800: 'boost::lockfree::detail::ringbuffer_base<T>::size_t' : forcing value to bool 'true' or 'false' (performance warning)

Pull request with fix submitted.

[timblechmann]

merged