[erlang-patches] Let epmd ignore empty ERL_EPMD_ADDRESS

[Holger Weiß]

By default, epmd listens on all available network interfaces.  However,
if it's executed using the following command line (in a Bourne Shell),
epmd currently listens only on the loopback interface:

    $ ERL_EPMD_ADDRESS='' epmd

FreeBSD PR #158357 is an example of how this can lead to unexpected
behaviour in practice:

    http://www.freebsd.org/cgi/query-pr.cgi?pr=158357

The following patch lets epmd ignore ERL_EPMD_ADDRESS if it's set to the
empty string:

    git fetch git://github.com/weiss/otp.git ignore-empty-epmd-address

Holger