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.

clean.do

@@ -6,7 +6,7 @@ if [ -e .do_built ]; then
 	done <.do_built
 fi
 [ -z "$DO_BUILT" ] && rm -rf .do_built .do_built.dir
-rm -rf minimal/.do_built minimal/.do_built.dir docs.out
+rm -rf minimal/.do_built minimal/.do_built.dir minimal/y docs.out
 redo t/clean docs/clean redo/clean
 rm -f *~ .*~ */*~ */.*~ *.pyc install.wrapper
 find . -name '*.tmp' -exec rm -f {} \;