Convert tincd path args to absolute paths

Convert tincd path args to absolute paths

Since tincd chdirs to its own configuration directory and only then
resolves relative paths passed as command-line arguments (like --config
and --pidfile), statements like these:

	$ tinc -c confdir init foo
	…
	$ tincd -c confdir -D

didn't work properly.

Now we resolve paths to absolute right when we receive them, and only
then do chdir.