Add LIBEVENT_LIBS to libafdt_la_LIBADD
Add LIBEVENT_LIBS to libafdt_la_LIBADD

This is apparently the proper mechanism for expressing that one library
depends on another.  The dependencies are now automatically added to our
programs' link.

linearregression/libafdt,facebook/libafdt,linearregression/libafdt,facebook/libafdt,linearregression/libafdt,facebook/libafdt