Update 2.6.txt

The link to list all backward breaking changes in Jira no longer works, we have switched from:

"Backward Breaking"

To:

"Backwards Compatibility"

And hence the parameters have switched.  The proposed change rectifies this for the 2.6 release notes

Signed-off-by: Sam Kleinman <samk@10gen.com>
Update 2.4.txt

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-2336: adding paragraph break
restructure page