Fixes Savannah bug #58883.

* configure.ac: Test for check >= 0.9.10.
* tests/argstr.c, tests/basic.c, tests/exec.c, tests/inspect.c,
tests/pump.c, tests/read.c, tests/redirect.c: Replace uses of
fail_unless and fail_if with appropriate ck_assert_* calls.  In most
cases these now use more specific equality etc. tests rather than just
passing arbitrary predicates.
* README: Document updated dependency.
* NEWS: Document this.