Tweak and/or extend some `acloca*.test' tests.

Tweak and/or extend some `acloca*.test' tests.

* tests/aclocal8.test:  Ensure verbose printing of captured
output.
* tests/aclocal.test: Likewise.  Also, add trailing `:'
command.
* tests/acloca19.test: Likewise.
* tests/aclocal5.test: Add trailing `:' command, and prefer
`$me' over hard-coded test name.
* tests/aclocal6.test: Likewise.
* tests/aclocal18.test: Add trailing `:' command, and make
some grepping slighty stricter.
* tests/acloca14.test: Likewise.  Also, prefer `diff' over
`cmp', and add some "cosmetic" blank lines.