Argp: fix recognition of short alias options.

Argp: fix recognition of short alias options.

* lib/argp-parse.c (convert_options): Fix improper use of
`|' between character values.
* tests/test-argp.c (group1_option): New alias option
--read (-r).
(group1_parser): Special handling for 'r'.
(test15): New test case.
(test_fun): Add test15.
* tests/test-argp-2.sh: Update expected --help and --usage
outputs.