Really abort when zlib is not found
Whitespace
Adopt parallel test harness of automake >= 1.12

If lower automake versions are used, the tests do not use mpirun
anymore.  We could have forced 1.12 in AM_INIT_AUTOMAKE, but then
this might inconvience the casual developer.

tl;dr: If you want mpirun -np 2 in tests, upgrade your automake.
Remove obsolete ARG_NOT_GIVEN_DEFAULT
Remove unused ARG_WITH_YES macros