Fix more inconsistent behaviour with symlinks in paths.

Both redo and minimal/do were doing slightly weird things with
symlinked directories, especially when combined with "..".  For
example, if x is a link to ., then x/x/x/x/../y should resolve to
"../y", which is quite non-obvious.

Added some tests to make sure this stays fixed.

t/.gitignore

@@ -3,5 +3,7 @@
 /shellfail
 /shelltest.warned
 /shelltest.failed
+/shlink
 /stress.log
+/symlink path
 /flush-cache