I'm a humble indirect user of Open-MPI. On OSX, my Open-MPI installation is supplied by the Homebrew package manager . Another package supplied by Homebrew is libevent.
I recently read on the dev list  a discussion about libevent having always been part of Open-MPI but being more apparent in 1.7.3.
At least on OSX, this causes unfortunate header file conflicts. If a user were to install both libevent and Open-MPI by hand to /usr/local (which is essentially what Homebrew does), one of the two would obliterate the 'event2' header files of the other. As far as I can tell, the 'event2' header files in Open-MPI differ from those in libevent 2.0.21 (the version currently distributed in Homebrew). This kind of conflict was absent from Open-MPI 1.6.
Homebrew supplies Open-MPI 1.7.3 by default because the compilers shipped with the latest OSX development environment (Xcode 5.0) fail to build Open-MPI 1.6.5 correctly (I do not use those compilers myself, but I am told `make check` fails) .Â
In view of the header file conflict, I'm wondering if there is a strong argument for not keeping the libevent-related header files of Open-MPI private. Stashing libevent-related stuff to a private location could probably be done more easily than adding logic to build Open-MPI against an external libevent.Â It's unfortunate for Open-MPI to conflict in this way with seemingly unrelated software packages that rely on libevent (e.g., tmux).