Merge branch 'trac5325' and added rules for files
    missed in asiolink:

src/lib/asiolink/Makefile.am
    +libkea_asiolink_la_SOURCES += io_acceptor.h
    +libkea_asiolink_la_SOURCES += unix_domain_socket_acceptor.h
    +libkea_asiolink_la_SOURCES += unix_domain_socket_endpoint.h