Support symlinking to dart-sdk executables on Linux and Mac.

sdk/bin/dart

Index: sdk/bin/dart
diff --git a/sdk/bin/dart b/sdk/bin/dart
index 22abed8b5e623c3425c39b9798a3754f58c309c8..eab8603b7de39a0160a920531edd18a4390020dd 100755
--- a/sdk/bin/dart
+++ b/sdk/bin/dart
@@ -4,8 +4,10 @@
 # BSD-style license that can be found in the LICENSE file.
 
 # Setting CUR_DIR this way is ugly, but is needed to handle the case where
-# sdk/bin has been symlinked to. On MacOS, readlink doesn't work with this case.
-CUR_DIR="$(cd "${0%/*}" ; pwd -P)"
+# sdk/bin or the script itself has been symlinked to. On MacOS, readlink -f
+# doesn't work with this case.
+SCRIPT=`readlink "$0" || echo "$0"`
+CUR_DIR="$(cd "${SCRIPT%/*}" ; pwd -P)"
 
 if [ -z "$DART_CONFIGURATION" ];
 then