add few basic regression tests

Most notably script running is not tested, but it is a difficult one to
make work without changing script directory.  I need to create another
version of command with compiler #ifdef and check_PROGRAMS that allows
script directory overriding.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
add pid file path to error message

Didn't I already do this in commit be7979b?  Oh well, maybe I did miss
this message earlier.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
remove obsolete gnulib module

Signed-off-by: Sami Kerola <kerolasa@iki.fi>