rrdcached: arrange option flags in order

To make it easier to determine which argument flags are available, the
getopt optstring is sorted into ASCII order.  Checking this against the
documentation indicated several supported flags were not present in the
synopsis.  Also make all flags bold for consistency.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
rrdtool: fix mis-use of getuid

Checking whether the application is running with root privileges requires
use of geteuid(), not getuid().

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
rrdcached: add options to drop privileges after daemonize

Some init systems have an interface to run daemons as unprivileged
accounts, but they conflict with rrdcached's expectations of creating
pid files and sockets in privileged areas when following Filesystem
Hierarchy Standard namings.  Add options that are used to drop to
unprivileged group and accounts after all activities that require
privilege have been completed.

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
rrdcached-lsb: update to support unprivileged group/user configuration

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
Merge pull request #501 from pabigot/enh-unpriv-rrdcached

rrdcached enhancements to drop unused privileges