* io/Makefile (test-srcs): Add ftwtest.
(distribute): Add ftwtest-sh.
(tests): Call ftwtest-sh for this goal.
* io/ftwtest-sh: New file. Sets up test environment, calls test
program and compares the result.
* io/ftwtest.c: Test program for ftw.
* misc/search.h: Add comments. Declare tdestroy.
* misc/tsearch.c (tdestroy): New function.
