Eliminate use of boost::lambda with boost::function (Trac #10864).

https://svn.boost.org/trac/boost/ticket/10864
I've used boost::lambda with boost::function in a number of creative ways over
the years. But the clang 6 shipped with Xcode 6 seems to have somehow broken
lambda + function in Boost 1.57. boost::phoenix is a partial workaround.
Sadly, lambda's comma-operator overload doesn't seem to be supported,
necessitating a couple ugly workarounds.
With real lambdas now supported by current compilers, I'm sure the Boost
community has little incentive to repair the lambda + function problem.
Presumably we'll be able to use such features ourselves Real Soon Now...