sample-config: Generate at build time

The old code generated sample configs full of "${prefix}", which is not
a variable naemon knows how to parse.

While we're at it, install the sample config as part of "make install",
but don't install it if the target config directory already exists.

Signed-off-by: Robin Sonefors <ozamosi@flukkost.nu>
configure: Install into standard prefix by default

This means /usr/local, rather than /usr/local/naemon. As part of doing
this, also install the config into $sysconfdir/naemon rather than just
$sysconfdir, as the latter just became /usr/local/etc by default (or
/etc, when --prefix is /usr), and we shouldn't litter that directory.

Signed-off-by: Robin Sonefors <ozamosi@flukkost.nu>
Makefile.am: Install everything by default

This should ensure that after "make install", you can start naemon or
install the init script straight away, without needing to create
files/directories that were required but weren't created.

Signed-off-by: Robin Sonefors <ozamosi@flukkost.nu>