edited CMakeLists.txt file to allow for c++11 compatibility with Xcode

also changed minimum OSX version to 10.8

@chrisdembia @sherm1 @aymanhab There are a couple lines in the file that we edited that said something like "CMAKE_CXX_FLAGS "-mmacosx-version-min=10.8 -m32"" (was previously ... 10.4 -m32). What does the -m32 flag mean, and does it still need to be there? Can still compile in Xcode and using unix makefiles with those lines commented out.