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

sdk/bin/pub

Index: sdk/bin/pub
diff --git a/sdk/bin/pub b/sdk/bin/pub
index 231da3ebc4cbc2580e647e355e622608a6fa7ab5..b8c761e79941b5cc759567fe70ba3dbf9aaad61f 100755
--- a/sdk/bin/pub
+++ b/sdk/bin/pub
@@ -7,9 +7,10 @@
 # structure.
 
 # 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)"
+# dart-sdk/bin or the script itself has been symlinked to. On MacOS, readlink -f
+# doesn't work with this case.
+SCRIPT=`readlink "$0" || echo "$0"`
+BIN_DIR="$(cd "${SCRIPT%/*}" ; pwd -P)"
 SDK_DIR="$(cd "${BIN_DIR}/.." ; pwd -P)"
 
 SNAPSHOT="$BIN_DIR/snapshots/pub.dart.snapshot"
@@ -40,4 +41,4 @@ else
   PUB="$SDK_DIR/lib/_internal/pub/bin/pub.dart"
 
   exec "$DART" "--package-root=$PACKAGES_DIR" "$PUB" "$@"
-fi
+fi