Create a little regression test framework for cp(1).
- wc(1) doesn't print a filename when reading from stdin.
- quote a string in ckl() - readlink(1) prints nothing if its argument
  doesn't exist.
- name tests in the same way that the sh(1) regression tests do.
Set OK before each test.
Use 'local' for local variables.
Add some tests for cp(1)'s -f flag. At the moment one of them is failing
because of a bug in cp(1).