Add support to enable LIBRAW_CALLOC_RAWSTORE

[perdrix52]

LibRaw 0.23.1 has added a new compilation definition LIBRAW_CALLOC_RAWSTORE.

Given that this is a compiler define that will do no harm on earlier release and is otherwise benefical it could be added unconditionally, Or if you wish controlled by an option in the CMakeLists.txt file.

What do you think?
David

[letmaik]

Feel free to add a new CMake option, no need to add a version check.

[perdrix52]

I know enough CMake to use it, and am beginning to to write my own simple CMake files, but don't think I have the skills to do this yet.