Won't build with clang 5+ on OSX

[aldanor]

Because unordered_map is no longer in tr1 namespace in libc++ (see e.g. https://groups.google.com/forum/#!topic/ceres-solver/RWAvy0TbI4A or http://stackoverflow.com/questions/7870897/why-some-include-files-only-reside-in-tr1)

In file included from src/engine.cc:13:
src/engine.hh:22:10: fatal error: 'tr1/unordered_map' file not found
#include <tr1/unordered_map>
         ^
1 error generated.
error: command 'clang' failed with exit status 1

One way to handle this on all platforms, I guess, is to use unordered_map from boost (since boost is used already anyway).

[dsacre]

Thanks! At some point I'll probably switch to C++11 which has <unordered_map>, but for now using the boost implementation seems like a good idea.

[aldanor]

You're welcome :) Looks like everything mostly works fine on OSX 10.9 now. I've discovered some sysex-related issues by the way, will post later if you're interested.

[aldanor]

Closed via #2.

[dsacre]

Please do! It's good to know mididings is usable on OSX :)