Improve and extend tests on canonicalization.

Improve and extend tests on canonicalization.

* tests/canon-name.test: Add trailing `:' command.  When writing
configure.in, prefer to use $me instead of hard-coding the test
name.
* tests/canon3.test: Prefer trailing `:' over trailing `Exit 0'.
* tests/canon4.test: Likewise.  Make grepping of Makefile.in
stricter.  Improve heading comment, and add reference to ...
* tests/canon6.test: ... this new test (sister test of the
previous one).
* tests/canon.test: Prefer cat + here-doc over echo to append
text to configure.in.  Extend grepping of Automake stderr.  Add
trailing `:' command.
* tests/canon5.test: Likewise.
* tests/canon7.test: New file, stress test on canonicalization.
* tests/canon8.test: New test, for better coverage (check that
the `@' character is not transliterated in canonicalizations).
* tests/Makefile.am: Updated.