set 8.1.5 release date in the manual: April 15, 2014.
Revert "version history for #3850"
This ticket has been revised to be in version 8.1.6.

This reverts commit 06b167a17fb23d2fc53ac7e4be0016bfcdca274c.
add 8.1.5 version history item for #4237
minimal documentation for new transaction() python binding. #4225