Forward ports from 2.4, Various janitor bits, and some fixes by me to
make the thing work again in 2.5.  I munged the MTDRAM driver to work
also (seperate patch to follow), and it seems to work.

David Woodhouse gave this the once over, and approved the changes.
Complete changelog below:

o   Don't create two slabcaches with the same name.
o   Don't corrupt eraseblock lists on mount
o   Don't mark nodes obsolete during mount
o   __attribute__((packed)) on the node definitions.
o   Fix up() without down() in jffs2_readdir().
o   Fix duplicate version number usage - s/highest_version++/++highest_version/
o   Fix (i.e. implement) mtime/ctime on directories.
    maybe too busy with the bk stuff
o   Don't allow hardlinks of directories.
o   s/(mode&S_IFMT)==S_IFLNK/S_ISLNK(mode)/ et al to keep Al happy.
o   Fix for garbage-collection of holes, where we used to write nodes out
    with csize/dsize swapped. Workarounds for existing such brokenness.
o   Improve wear levelling by rotating node lists on mount, to avoid starting
     at one end of the flash every time.
o   Remember to get internal inode-semaphore on symlink operations.