units: an alternative script for test.units target of testing.mak

test.units target is too complex.
The test cases are run sequentially. So I rewrite it as a shell script.

Some features not in the test.units are implemented.

1. It can run tests under timeout command.
   Under timeout command all test cases classed to .i(entering infinite
   loop) are run.

2. It can run tests under valgrind.
   all test cases classed to .v are run but the results are ignored.

3. It checks exit status of each running of test cases.
   If the status is not 0, the test is treated as "FAILED".
   If expected.tags file is not prepared in a test, units command checks
   only the exit status.

4. It deals a sub-directory as a category.
   It is proposed by @ffes in #88.
   A directory ended with .r is recognized as a category.
   This feature isn't tested yet.

5. It reports "FIXED".

   If a .b class test(known bug) is passed, it is reported as FIXED.
   If a .i class test(infinite loop) is passed with --with-timeout option,
   it is reported as FIXED.

You can run units with

    $ make -f testing.mak units

UNIT_LANGUAGE and UNIT macros can be used like

    $ make -f testing.mak units UNIT_LANGUAGE=C UNIT=local.c

Signed-off-by: Masatake YAMATO <yamato@redhat.com>