s/B_FIND_PATH_IMAGE_PACKAGE_PATH/B_FIND_PATH_PACKAGE_PATH/

It doesn't only work for image files, so make the name more general.
find_path_for_path_etc(): Fail for B_FIND_PATH_IMAGE_PATH

There's no image in this case. We would just return the path we were
given.
BPathFinder: Coding style improvements
Add find_path*() API docs, improve FindDirectory.h docs
Add get_*architecture*() API docs
Add BPathFinder API docs