Fix issue 3402 . The initial suggestion of using readlink doesn't

utils/compiler/build_helper.dart

Index: utils/compiler/build_helper.dart
===================================================================
--- utils/compiler/build_helper.dart	(revision 12972)
+++ utils/compiler/build_helper.dart	(working copy)
@@ -103,7 +103,11 @@
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
-BIN_DIR=`dirname \$0`
+# 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 "\$(dirname "\$0")"; pwd -P`

[ahe, 2012/09/28 03:47:30]

I've been reading up on the Bash manual
(http://www.gnu.org/software/bash/manual/bashref.html#Positional-Parameters)

As far as I can tell, there is no guarantee that $0 is an absolute path.
However, $_ is. So I prefer this version:

# Must be first command in this script.
ABS_SCRIPT_PATH="\$_"
BIN_DIR="\$(cd "\${ABS_SCRIPT_PATH%/*}" ; pwd -P)"

The advantage to ${ABS_SCRIPT_PATH%/*} over dirname ${ABS_SCRIPT_PATH} is that
it relies solely on bash built-in commands. This should make the script faster
(I'm actually seeing "dirname" showing up in the title of my Mac Terminal app
sometimes).

[dgrove, 2012/09/28 15:48:17]

This seems like a good (but even uglier) alternative. I went ahead and switched
to this.

+
 unset COLORS
 if test -t 1; then
   # Stdout is a terminal.