build-sys: fix double prefix with explict --libdir

* with configure --prefix=$HOME --libdir=$HOME usrlib_execdir
  ends up being ${exec_prefix}/${libbir}, which is double-prefixed

* fix: use explict given ${libbir} if is matches ${prefix}/*

Signed-off-by: Christoph Junghans <ottxor@gentoo.org>
docs: restore the mention of uhelper= and helper= in man page of umount

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
tests: kill output message change

Commit 09af3db48e01e5744f15fd8a2395e0fed36526ea changed how a missing
process is reported, which caused kill test to fail when the test suite
is ran as root.

Reference: https://travis-ci.org/karelzak/util-linux/jobs/31312170
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
zramctl: fix the wording of some message strings

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
docs: improve the wording and formatting of the zramctl man page

Especially fix the mistaken short option -h for --noheadings.

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>
Merge branch 'master' of https://github.com/ottxor/util-linux