Tests: normalize use of the 'errexit' shell flag. * tests/maken3.test (check_targets): Remove redundant call to 'set -e'. * tests/maken4.test: Likewise. * tests/ansi5.test: Call 'set -e' just after './defs' has been sourced. * tests/ansi6.test: Likewise. * tests/ansi7.test: Likewise. * tests/cond16.test: Likewise. * tests/cond17.test: Likewise. * tests/cond18.test: Likewise. * tests/cond19.test: Likewise. * tests/cond20.test: Likewise. * tests/cond21.test: Likewise. * tests/instdat2.test: Likewise. * tests/instdir-texi.test: Likewise. * tests/parallel-tests3.test: Likewise. * tests/remake1a.test: Likewise. * tests/ccnoco.test: Likewise, and add trailing `:' command. * tests/comment4.test: Likewise. * tests/gcj4.test: Likewise. * tests/nodist2.test: Likewise. * tests/nodist3.test: Enable 'errexit' shell flag (this should have been done in commit v1.11-248-g317e17b, but the relevant hunk has been forgotten somehow). * tests/output.test: Likewise. * tests/gnits2.test: Likewise, and display captured stderr to script's stderr, not to script's stdout. * tests/gnits3.test: Likewise. Also, prefer 'cat' over 'echo' to append to Makefile.am, and really check that the exit status of "make installcheck" indicates failure.