prepare for Mac OS 10.10 (Yosemite)

One thing to notice is the setting of the environment variable
MACOSX_DEPLOYMENT_TARGET, described in M2/INSTALL.
Fix issue https://github.com/Macaulay2/M2/issues/164, add test for it
Merge branch 'master' of https://github.com/Macaulay2/M2 into experimental
redo fix of #196 due to me being dumb
merge change from master