src/cache/ftcsbits.h, src/cache/ftcmanag.h, src/cache/ftccmap.h,
src/cache/ftcmru.h: copying the cache's internal header files which
were located in 'include/freetype/cache' to the 'src/cache' directory
instead.
Note that these files are not used by FreeType clients, all cache
public APIs have been already moved to include/freetype/ftcache.h,
and the FT_CACHE_INTERNAL_XXXX_H macros all resolve to it.
the move is to allow us to modify the internals without intereference
from rogue clients. Note that there are no known client that accesses
the cache internals at the moment.
