log* tests: More tests.

* tests/test-log.h: New file.
* tests/test-log.c: Include <float.h>, minus-zero.h, test-log.h.
(main): Invoke test_function.
* tests/test-logf.c: Include <float.h>, minus-zero.h, test-log.h.
(main): Invoke test_function.
* tests/test-logl.c: Include <float.h>, minus-zero.h, test-log.h.
(main): Invoke test_function.
* modules/log-tests (Files): Add tests/test-log.h, tests/minus-zero.h,
tests/randomd.c.
(Makefile.am): Add randomd.c to test_log_SOURCES.
* modules/logf-tests (Files): Add tests/test-log.h, tests/minus-zero.h,
tests/randomf.c.
(Makefile.am): Add randomf.c to test_logf_SOURCES.
* modules/logl-tests (Files): Add tests/test-log.h, tests/minus-zero.h,
tests/randoml.c.
(Depends-on): Add 'float'.
(Makefile.am): Add randoml.c to test_logl_SOURCES.