build and tests: curl_10char_object_name() shell function

lib/objnames.inc provides definition of curl_10char_object_name() shell
function. The intended purpose of this function is to transliterate a
(*.c) source file name that may be longer than 10 characters, or not,
into a string with at most 10 characters which may be used as an OS/400
object name.

Test case 1221 does unit testng of this function and also verifies
that it is possible to generate distinct short object names for all
curl and libcurl *.c source file names.

lib/objnames-test.sh is the shell script used for test case 1221.

tests/runtests.pl modified to accept shell script test cases.

More details inside lib/objnames.inc and lib/objnames-test.sh