Ensure proper path traversals for linked commands;

sdk/bin/dartdoc

Index: sdk/bin/dartdoc
diff --git a/sdk/bin/dartdoc b/sdk/bin/dartdoc
index 3f223678f655240fa886e78badda0250211bdfb8..0b00408468262d87b9303aaffaac1360fe516b5c 100755
--- a/sdk/bin/dartdoc
+++ b/sdk/bin/dartdoc
@@ -6,7 +6,16 @@
 # Setting BIN_DIR this way is ugly, but is needed to handle the case where
 # dart-sdk/bin has been symlinked to. On MacOS, readlink doesn't work
 # with this case.
-BIN_DIR="$(cd "${0%/*}" ; pwd -P)"
+function link_dir() {
+  a="$1"
+  while [ -h "$a" ]; do
+    # On Mac OS, readlink -f doesn't work.
+    a="$(readlink "$a")"
+  done
+  # if dir linked, not file, need to follow dir path:
+  echo $(cd $(dirname $a); pwd -P)
+}
+BIN_DIR="$(link_dir "$0")"
 
 unset COLORS
 if test -t 1; then