Minor: little typo fix

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-1742: amount of space used by compaction
findAndModify edits
copy edit findAndModify subheading
DOCS-1743: correcting sources of confusion for mongodump/mongorestore with replica set members
Update expire-data.txt

Clarifying how Mongo handles documents under a TTL index, that omit the indexed column.

Signed-off-by: Sam Kleinman <samk@10gen.com>
index-reorg: initial pass & toc-tree-ification
index-reorg: adding index reference section
build: fixing table generation
index-reorg: correcting reference table sadness
index-reorg: more breaking up of concepts