These war files are built every night automatically off of the code in our subversion repository. If the database schema has changed, you will need to "source" the update-to-latest.sql file on your database. (Note: The files are only built if there was a commit to SVN within the past 24 hours.) . Note that the build/revision number can be seen at the end of the api jar version number.
Download nightly releases from Sourceforge.net: http://sourceforge.net/projects/openmrsdev/files/nightly/