bug#16121: 24.3.50; Type error in ERT

[Sebastian Wiesner]

`ert-select-tests' tries to match a symbol against a string with
`string-match', causing a `wrong-type-argument' error.

The culprit is in the `string' branch of the `cl-etypecase' expression,
where the following expression is used as predicate for
`cl-remove-if-not':

(and (ert-test-name test)
     (string-match selector (ert-test-name test)))

However, `ert-test-name' returns a *symbol* with the name of the test.

The error is fixed by applying `symbol-name' to the return value of
`ert-test-name':

(and (ert-test-name test)
     (string-match selector (symbol-name (ert-test-name test))))