Simplified the directory cache size change functionality.

Added the CACHETABLES option, which tells smbfs how many individual directory caches it should be using (default: 1). Each directory cache can be used by one directory at a time.
If you are deleting a directory tree, including subdirectories, etc. then smbfs will be limited in keeping track of what it deleted, and what directory is next up for deletion.
With only a single directory cache, it will be limited to deleting a subdirectory's contents, but forget about its parent directory, for example, and thereby end up skipping entries which should have been deleted.
This can be annoying because you will have to repeat the delete operation several times over until everything has been deleted. Increasing the number of cache tables can help, at the expense of extra memory.
Increasing the number of cache tables can also improve performance if several programs are examining the contents of directories at the same time.