Libevent configuration doesn't use pkg-config
This interferes with some packages/ports (e.g. OpenBSD's) because the system's libevent CFLAGS and LIBS aren't used.
Pkg-config would probably make the dev's lives easier, too. Because the project is dropping support for older libevent versions, now's a good time.
Thoughts? Would this break any non-Unixy platforms?