Fix iop/cp test

Change permissions before checking for them to ensure we can affect
them.

The test didn't pass for umask == 077.

Thanks to filterfalse.
Merge branch 'make-one-io-test-less-error-prone'

Fix one of tests for umask == 077.

Thanks to filterfalse.
Allow absolute paths as arguments for executable()

Thanks to filterfalse.
Merge branch 'allow-abspath-for-executable-func'

Allow absolute paths as arguments for executable().

Thanks to filterfalse.