fix libraw for windows using visual studio 2010

libraw.h was not found when a custom LIBRAW_PATH was specified. This is due to the header file being located in the /libraw subfolder. When using PATH_SUFFIXES in FIND_PATH the specified suffix is added to the path passed via -I to the compiler. rawinput.cpp correctly uses #include <libraw/libraw.h>. This results in the compiler searching for the libraw.h in /libraw/libraw/libraw.h. Solved by moving the suffix to the search path.

log2f is not defined in VS < 2012