librrd.sym: add rrd_scaled_duration

This librrd function was found when linking executables where main() was
in a libtool convenience library, but not when linking rrdcached.  The
solution is to add it into the secret file that specifies which files
are part of the public API.
rrdcached: support duration specifiers in command-line arguments

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
rrdcached: support wildcard listen specifications

The documentation suggested that the syntax "-l :42217" would cause the
daemon to listen on all available interfaces.  The implementation didn't
follow through, until now.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
rrd_daemon: move include of arpa/inet.h to avoid use on Windows

arpa/inet.h may not be available on Windows systems; since I can't test
that, avoid trying to include it there.  Since the code that depends on
it is conditional on a define that would be provided by it, there should
be no impact from its absence except that somebody who uses Windows
would have to rework the fix for ipv4-over-ipv6 for that platform.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
rrdcached: support new option to listen on all addresses at default port

This functionality can be achieved with "-l ''" (specifying an empty
string for host:port) but empty strings may be dropped during option
processing in scripts.  A separate option to support this capability is
much more clear.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
Merge pull request #489 from pabigot/enh-rrdcached

rrdcached enhancements