Notify as soon as build fails

[2shortplanks]

I'd like to know as soon as the build fails - i.e. when it starts failing, rather than waiting for completion.

I think it should be as simple as overriding the [buildChangedStatus](http://javadoc.jetbrains.net/teamcity/openapi/8.0/jetbrains/buildServer/serverSide/BuildServerAdapter.html#buildChangedStatus%28jetbrains.buildServer.serverSide.SRunningBuild, jetbrains.buildServer.messages.Status, jetbrains.buildServer.messages.Status%29) method in SlackServerAdapter

Thoughts?