Build fails with "ERROR: Your JAVA_HOME environment variable is set"

[Matthew Flaschen]

A build of latest hg fails with:

ERROR: Your JAVA_HOME environment variable is set.  This will
       most likely cause the build to fail.  Please unset it
       and start your build again.

Exiting because of the above error(s).

Should this need to be unset?  I think I've always built with it set in
the past.

Matt Flaschen