[JFFS2] Check CRC32 on dirent and data nodes each time they're read

Also, make sure dirents are marked REF_UNCHECKED when we 'discover' them
through eraseblock summary.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

diff --cc fs/jffs2/readinode.c
Simple merge

diff --cc fs/jffs2/summary.c
Simple merge