Bump version to 0.9
Fix auto-enabling of developer mode

With the merge of the various Kyua modules into a single repository,
the .git directory now lives one level up and the automatic enabling
of the developer mode broke because of this.  Just fix the path.
Fix a couple of Doxygen warnings

There are some more left but I cannot figure out how to resolve them yet.
Remove extra trailing dot

Command descriptions should not end with a dot because the cmdline
library adds one when generating the usage message.
Fix test under FreeBSD

It turns out that doing an exec*("dir/foo") when dir/foo does not
exist but dir/ has 0000 permissions results in an ENOENT error in
FreeBSD, while according to the documentation and other systems it
should be EACCES.

I suspect this is a bug in FreeBSD but, to make the test less
ambiguous, just make the binary itself inaccessible instead of the
parent directory.
Remove unused function

Spotted by clang 3.4 in FreeBSD 11.0-CURRENT.
Remove empty test programs

There really is no point in adding test programs as placeholders with
a single "TODO" test case.  These haven't been addressed for years and
won't be anytime soon.