Fix tutorial includes for Apple platform
Fix printDevices: A parameter was missing.
Fix Clang build

Clang automatically deletes assign-operator if a copy constructor is defined. To make the library build with Clang, add the assign-operator GNU-G++ would add automatically.

This way, the code compiles with Clang and the change has no impact on GNU-G++.
Include math.h file

G++ automatically includes this, but Clang complains about missing function declarations.

Again, this has no impact on GNU-G++ but makes the library build on Clang
Check if CL_KHR_ICD is available

This optional package is not included in OS X, so the library did not build.
Merge pull request #2 from nischu/osx-fixes

Some fixes for Clang/OS X