Modernize, improve and/or extend tests `colon*.test. * tests/colon.test: Rely on the `configure.in' stub created by `./defs', rather than writing one from scratch. Do not create a useless dummy file. Add trailing `:' command. * tests/colon4.test: Enable the `errexit' shell flag, and related changes. Rely on the `configure.in' stub created by `./defs', rather than writing one from scratch. * tests/colon7.test: Enable `errexit' shell flag, and related changes. Improve the generated `configure.in' file. Add trailing `:' command. * tests/colon2.test: Likewise. Also, add some new checks. * tests/colon5.test: Improve the generated `configure.in' file. Add new, much deeper checks. Add trailing `:' command. * tests/colon6.test: Likewise. * tests/colon3.test: Improve the generated `configure.in' file. Prefer perl over pipelined grep. Made stricter. Other changes, cosmetic and not.