DOCS-3016: adding link to mongodb world
trivial: fix various build warnings and errors
DOCS-3014 copy-edits for intro to agg command
"minor: 2.6 compatibility cross referencing"

This reverts/modifies commit 11156f83a707847f093a4ff85eecb0c1445e8dd8.
Don't suggest using a collection name with a dot

Signed-off-by: kay <kay.kim@10gen.com>
DOCS-2973 add Drivers to left hand nav