Append $(EXEEXT) to programs that may be listed in TESTS.

Append $(EXEEXT) to programs that may be listed in TESTS.
Report from Simon Josefsson.

* automake.in (%known_programs): New global.
(initialize_per_input): Reset it.
(append_exeext): Take a predicate as first argument to select
the filename to rewrite.
(handle_programs): Fill %known_programs.
(handle_tests): Append $(EXEEXT) to all tests that are in
%known_programs.
(am_install_var): Update call to append_exeext.
* doc/automake.texi (EXEEXT): TESTS is also rewritten.
(Tests): More about the difference between check_PROGRAMS and TESTS.
Give an example of TEST_ENVIRONMENT.
* tests/cond32.test: Augment with a nested condition.
* tests/exeext4.test: Also check TESTS.
* tests/check5.test: New file.
* tests/Makefile.am (TESTS): Add check5.test.