[PATCH] ext3: more comments about block allocation/reservation code

Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>