Makefile: DESTDIR support for all install* targets

Signed-off-by: Andreas Beckmann <anbe@debian.org>
set 'prefix' and 'DESTDIR' for build and install targets

Signed-off-by: Andreas Beckmann <anbe@debian.org>
lib/read_config.sh: get_config_value() used by all master/slave scripts

factored out the shell function currently embedded in {master,slave}-bin/*
installed as $prefix/share/piuparts/lib/read_config.sh
shipped in piuparts-common.deb

Signed-off-by: Andreas Beckmann <anbe@debian.org>
Makefile: add support for placeholders in scripts

e.g. @sharedir@ to find read_config.sh

Signed-off-by: Andreas Beckmann <anbe@debian.org>
master/slave-bin: rename * -> *.in to allow substitutions

Signed-off-by: Andreas Beckmann <anbe@debian.org>
source read_config.sh instead of embedding a copy of get_config_value()

Signed-off-by: Andreas Beckmann <anbe@debian.org>
read_config.sh: support RFC822 wrapped+indented lines

it is also allowed to have non-indented comments between
wrapped+indented lines

python ConfigParser supports this, too
(and I really want to split+wrap the '[global] sections = ...' line)

Signed-off-by: Andreas Beckmann <anbe@debian.org>
add support for placeholder substitution in conffiles

prepare for inserting the correct absolute path at build time

Signed-off-by: Andreas Beckmann <anbe@debian.org>
use sharedir substitution in crontabs

stop using $HOME

Signed-off-by: Andreas Beckmann <anbe@debian.org>