Sanitize the regex test cases.

- Merge h_regex_att (att.c) and t_regex_att.sh into a single C test program.
The former was really a test program, and the latter just a very strange
driver for it

Sanitize the regex test cases.

- Merge h_regex_att (att.c) and t_regex_att.sh into a single C test program.
The former was really a test program, and the latter just a very strange
driver for it.

- Stop using awk to generate the shell test programs. This is unnecessary
and confusing. Instead, change t_regex.sh to generate the test case
functions on the fly with eval (as done in many other places).

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