I just installed the build-timeout plugin and it's mostly working, but
even with the "Fail the build" setting checked, my builds are still
being marked as "aborted":

For example, here is the tail of the console output:
{{
[...]
Build timed out (after 3 minutes). Marking the build as failed.
Terminated
+++ vncserver -kill beast:3 -clean
Killing Xtightvnc process ID 12328
+++ exit
Finished: ABORTED
}}

Note that it says it will fail the build, but then it is aborted and
the status of the build is set to aborted, not failed. Bonus pain:
Of course no email goes out.

This is with Jenkins ver. 1.404 and build-timeout ver. 1.7.