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

t/105-sympath/.gitignore

@@ -0,0 +1,5 @@
+/*.dyn
+/src
+/x
+/y
+

t/105-sympath/all.do

@@ -0,0 +1,31 @@
+redo-ifchange ../flush-cache
+rm -f src
+: >src
+
+for iter in 10 20; do
+	rm -rf y
+	rm -f x *.dyn static
+	mkdir y
+	: >y/static
+	ln -s . y/x
+	../flush-cache
+
+	(
+		cd y/x/x/x/x/x
+		IFS=$(printf '\n')
+		redo-ifchange static x/x/x/static $PWD/static \
+			$(/bin/pwd)/static /etc/passwd
+		redo-ifchange $PWD/../static 2>/dev/null && exit 35
+		redo-ifchange 1.dyn x/x/x/2.dyn $PWD/3.dyn \
+			 $PWD/../4.dyn $(/bin/pwd)/5.dyn
+	)
+	[ -e y/1.dyn ] || exit $((iter + 1))
+	[ -e y/2.dyn ] || exit $((iter + 2))
+	[ -e y/3.dyn ] || exit $((iter + 3))
+	[ -e 4.dyn ]   || exit $((iter + 4))
+	[ -e y/5.dyn ] || exit $((iter + 5))
+
+	# Second iteration won't work in minimal/do since it only ever
+	# builds things once.
+	. ../skip-if-minimal-do.sh
+done

t/105-sympath/clean.do

@@ -0,0 +1,2 @@
+rm -rf y
+rm -f src x *.dyn *~ .*~

t/105-sympath/default.dyn.do

@@ -0,0 +1,2 @@
+redo-ifchange src
+echo dynamic >$3

t/clean.do

@@ -2,6 +2,6 @@
 sed 's/\.do$//' |
 xargs redo
 
-rm -f broken shellfile shellfail shelltest.warned shelltest.failed \
-	*~ .*~ stress.log flush-cache
+rm -f broken shellfile shellfail shelltest.warned shelltest.failed shlink \
+	*~ .*~ stress.log flush-cache 'symlink path'
 rm -rf 'space home dir'

t/shelltest.od

@@ -474,6 +474,12 @@ set x y z
 x=$(printf "a%-5sc" "b")
 [ "$x" = "ab    c" ] || warn 119
 
+# Make sure cd supports -L and -P options properly
+rm -f shlink
+ln -s . shlink
+(cd -L shlink/shlink/shlink/../shlink) || fail 120
+(cd -P shlink/shlink/shlink/../shlink) && fail 121
+
 [ -e shelltest.failed ] && exit 41
 [ -e shelltest.warned ] && exit 42
 exit 40