Don't pass ${HOST} to test scripts.
htnl_cmp compares against the output of `hostname`.

This makes the tests pass on my machine.

- move special files defines into bozohttpd.h, so we can ...
- consolidate all the special file checks into
bozo_check_special_files() so that all builds check the same
list of special files, regardless of build options.
- convert "(void)bozo_http_error(...); return -1;" into plain
"return bozo_http_error(...);"
- fix the call to bozo_check_special_files() to be used on all
input types. part of the fixes for failure to reject access
to /.htpasswd as reported by JP on tech-security.
- use warn_unused_result attribute on bozo_check_special_files(),
and fix the failures to return failure. second part of the
htpasswd access fix.
- update testsuite to use a fixed fake hostname.

call this bozohttpd 20181121.

branches: 1.4.2; 1.4.4; 1.4.6; 1.4.10; 1.4.16; 1.4.18;
- fix a bug in cgi processing. from Dennis Lindroos.
- add a testcase for this, and expand test-simple to handle additional
args to bozohttpd for eg, cgi-bin setting.
- fix objdir bugs in the testsuite.

branches: 1.3.2; 1.3.4;
When testing non-verbosely, show diff on failure. ok mrg@

branches: 1.2.2; 1.2.4; 1.2.6;
Missed in previous: exit 1 if html_cmp says no match.

Add a VERBOSE knob to the testsuite ("yes" by default, producing
basically the same output as before). When turned off, tests run
silently except when there's a failure.

Reviewed by mrg@.