fixed bug that made camke ignore passed flag

Arguments passed to the configure script had quotation marks.
As a result some flags were ignored by cmake.
removed unused source file (actor_facade.cpp)
added configureable result buffer size to spawn_cl

This is a new argument for the function spawn_cl. It defaults to zero,
which causes the implementation to calculate the buffer size according
to the number of create work-items.

The simple matrix example sets the buffer size manually.
added pfn_notify callback to print error messages

removed build log from program, since it is printed by the callback
Added asynchronous call to read memory from GPU.

Blocking calls result in undefined behavior.
added compiler options to program

+ unit test in test_opencl
Added test for variable result size

... and fixed bug in variable result size.
improved readability of add_arguments_to_kernel

rotate buffer, instead of multiple function calls
added unit test for constant memory argument
changed cl_event handling in command

preparation for asynchronous copy operations to device
data copy to GPU is now asynchronous
Merge branch 'unstable' into topic/opencl

Conflicts:
	configure
	cppa/opencl/actor_facade.hpp
	cppa/opencl/command.hpp
Merge branch 'topic/opencl' into unstable