exp* tests: More tests.

exp* tests: More tests.

* tests/test-exp.h: New file.
* tests/test-exp.c: Include <float.h> and test-exp.h.
(main): Invoke test_function.
* tests/test-expf.c: Include <float.h> and test-exp.h.
(main): Invoke test_function.
* tests/test-expl.c: Include <float.h> and test-exp.h.
(main): Invoke test_function.
* modules/exp-tests (Files): Add tests/test-exp.h, tests/randomd.c.
(Makefile.am): Add randomd.c to test_exp_SOURCES.
* modules/expf-tests (Files): Add tests/test-exp.h, tests/randomf.c.
(Makefile.am): Add randomf.c to test_expf_SOURCES.
* modules/expl-tests (Files): Add tests/test-exp.h, tests/randoml.c.
(Depends-on): Add 'float'.
(Makefile.am): Add randoml.c to test_expl_SOURCES.