Use ck_assert_ptr_ne() instead of ck_assert(ptr != other_ptr)

Semantically they're the same, but this way looks neater and
more consistent.

Signed-off-by: Andreas Ericsson <ae@op5.se>
Revert "configure.ac: Make automake shut up about subdir-objects"

This reverts commit 122508243c1aaf7b54a530b89e53d6683f942e8b,
because apparently tests fail when subdir-objects is enabled.

Signed-off-by: Andreas Ericsson <ae@op5.se>