haproxy: explicitly enable USE_DL, that is required at least in Ubuntu 15.10.

component/haproxy/buildout.cfg

@@ -22,6 +22,7 @@ make-options =
   TARGET="$(uname -sr 2>/dev/null|grep -Eq '^Linux (2\.6\.2[89]|2\.6\.[3-9]|3)' && echo linux2628 || echo generic)"
   ARCH="$(uname -m 2>/dev/null|grep -E '^(x86_64|i[3456]86)$')"
   PREFIX=${buildout:parts-directory}/${:_buildout_section_name_}
+  USE_DL=1
   USE_LUA=1
   LUA_INC=${lua:location}/include
   LUA_LIB=${lua:location}/lib