Update bin/alh.sh

On Mac OS X, "readlink -f" isn't supported.  But "greadlink" (GNU readlink) works just fine.  This patch should fix the script for Mac users.

bin/alh.sh

@@ -2,6 +2,19 @@
 #
 # Start-up script
 
-L10N_HELPER_HOME="$(dirname "$(readlink -f "$0")")/.."
+L10N_COMMAND=readlink
+
+# Mac OS X doesn't support "readlink -f", but Homebrew offers a "coreutils" 
+# package that contains "greadlink" (GNU readlink)
+if [ `uname` = 'Darwin' ]; then
+    L10N_COMMAND=greadlink
+    if [ -z `which greadlink` ]; then
+        echo "greadlink not found. Please install it using homebrew:" 1>&2
+        echo "brew install coreutils" 1>&2
+        exit 1
+    fi
+fi
+
+L10N_HELPER_HOME="$(dirname "$($L10N_COMMAND -f "$0")")/.."
 
 java -jar $L10N_HELPER_HOME/lib/l10n-helper.jar $1 $2