DOCS-2227: New 2.6 Upgrade Doc

Signed-off-by: kay <kay.kim@10gen.com>
add auth procedures for 2.6 upgrade
making this document consistent with the system-users-collection document

Signed-off-by: Sam Kleinman <samk@10gen.com>
suggested wording change

Signed-off-by: Sam Kleinman <samk@10gen.com>
Update install-mongodb-on-os-x.txt

Update link to use new Brew website

Signed-off-by: Sam Kleinman <samk@10gen.com>
change text in UDR note from 2.5.3 to 2.5.4

Signed-off-by: Sam Kleinman <samk@10gen.com>
include ssl options to mongos