support multi-level symlinks to SDK exes

sdk/bin/pub

Index: sdk/bin/pub
diff --git a/sdk/bin/pub b/sdk/bin/pub
index 42f84fce029f3bf86b7b05916877c25dc8158b27..616ff42929068daa1aa96f72746b81d553363876 100755
--- a/sdk/bin/pub
+++ b/sdk/bin/pub
@@ -6,17 +6,15 @@
 # Run pub.dart on the Dart VM. This script assumes the Dart SDK's directory
 # structure.
 
-function follow_links() {
-  file="$1"
-  while [ -h "$file" ]; do
-    # On Mac OS, readlink -f doesn't work.
-    file="$(readlink "$file")"
-  done
-  echo "$file"
-}
-
-# Unlike $0, $BASH_SOURCE points to the absolute path of this file.
-PROG_NAME="$(follow_links "$BASH_SOURCE")"
+PROG_NAME=$(cd -P -- "$(dirname -- "$0")" && pwd -P) && \
+  PROG_NAME=$PROG_NAME/$(basename -- "$0")
+
+# resolve symlinks
+while [ -h $PROG_NAME ]; do
+    DIR=$(dirname -- "$PROG_NAME")
+    SYM=$(readlink $PROG_NAME)
+    PROG_NAME=$(cd $DIR && cd $(dirname -- "$SYM") && pwd)/$(basename -- "$SYM")
+done
 
 # Handle the case where dart-sdk/bin has been symlinked to.
 BIN_DIR="$(cd "${PROG_NAME%/*}" ; pwd -P)"