* src/files.c (tr): Change return type to void.

* src/files.c (tr): Change return type to void.
* src/muscle_tab.c (muscle_insert): Free storage in case muscle_grow
has been called previously for the same key.
(muscle_find): Return storage instead of value so that
--enable-gcc-warnings doesn't produce warnings that the return discards
const.  aver that the value and storage are the same since storage
could potentially be NULL when value is not.
* tests/testsuite.at (AT_CHECK): Treat an unspecified exit value the
same as 0.