include signal.h to avoid error: main.cpp:468:3: error: use of undeclared identifier 'sigemptyset'
link to boost system to avoid undefined symbol 'boost::system::system_category()'
add aclocal for boost system
Merge pull request #32 from springmeyer/osx-build-fixes

Fixes to compile and link on OS X
Fixed several warnings from -Wall.
Merge branch 'master' into gsoc13