Merge branch 'develop' of https://github.com/stan-dev/stan into develop
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
pass -DGTEST_USE_OWN_TR1_TUPLE via CFLAGS_GTEST in makefile

GTEST_USE_OWN_TR1_TUPLE needs to be defined when compiling Stan
with the libc++ library. Setting it in the top-level makefile
is easier and more consistent than setting it in each of the
make/os_* files.
Merge pull request #67 from stan-dev/feature/GTEST_USE_OWN_TR1_TUPLE

set GTEST_USE_OWN_TR1_TUPLE globally
Merge branch 'develop' into gp_improvements