Fix compilation on Mavericks
Merge remote-tracking branch 'origin/master' into feature/cocoa-mavericks
Use libstdc++ for boost (hat tip to @shayneski)
Merge branch 'master' into feature/cocoa-mavericks
gate libstdc++ inclusion on OS X release >= 13.0.0 (Mavericks)
reduce number of flags; use another mechanism for checking OS version
Merge pull request #76 from rstudio/feature/cocoa-mavericks

fix linker errors on Mac OS X Mavericks and later