Bugfix/build osx macports (#563)

Two MacPorts/gcc7 issues:

std::uint64_t is unsigned long long on OS X, breaking an assumption about size_t in the distributed_context interface.
Problems with missing errno defines in the standard library headers.
With MacPorts gcc7, the installed c++config.h defines _GLIBCXX_HAVE_EOWNERDEAD and _GLIBCXX_HAVE_ENOTRECOVERABLE, but the corresponding errno defines are not provided by
sys/errno.h unless __DARWIN_C_SOURCE, which takes its value from _POSIX_C_SOURCE if defined, is greater than or equal to 200809L. Technically a MacPorts configuration bug? but easily worked around.

Use basic integral types for communication collectives interfaces.
Define _POSIX_C_SOURCE to be 200809L for glob.cpp.
Fixes #562.