BOOST_ROOT not being picked up when doing pip build

[pmemon]

BOOST_ROOT is not being picked up when you do a "pip install ." on OS X so it isn't finding the include files and subsequently the boost library.

I am building this under a separate conda environment.

[riastradh-probcomp]

Should be fixed in 97913ad. Can you please test?

(Generally better to use CPPFLAGS/LDFLAGS for this, not project-specific BOOST_ROOT, but I guess the latter seems to be common in the anaconda world.)