Fix file-name problems in several tests

Fix file-name problems in several tests

* test/lisp/saveplace-tests.el
(saveplace-test-forget-unreadable-files):  Use file-truename, to
avoid false negatives when file names are not 'equal' as strings,
but point to the same file.
* test/lisp/emacs-lisp/edebug-tests.el (edebug-tests-with-normal-env)
(edebug-tests-run-macro):
* test/lisp/emacs-lisp/testcover-tests.el
(testcover-tests-markup-region, testcover-tests-run-test-case):
Bind find-file-suppress-same-file-warnings to  a non-nil value, to
avoid warnings about "same-file-names", at least on MS-Windows,
due to 8+3 aliases.