Add explanation on reIndex() fix typo on getIndexes

dropIndex doesn't work on _id which most indexes in config DB are. Also there was typo on db.collection.getIndexes().

Signed-off-by: Sam Kleinman <samk@10gen.com>
Fixed typo

Signed-off-by: Sam Kleinman <samk@10gen.com>
minor: edits
DOCS396, DOCS-1080, DOCS-1420, DOCS-1616 refactoring & updating production notes