dist: fix postinstall script for Darwin

The postinstall script causes the installation to fail because the last
step that copies files for Xcode is broken. Two details can cause the
command to fail:
  1. The XCODE_MISC_DIR value has a space. Without quotes in the cp
     command, cp will just complain that this is an invalid syntax.
  2. The source of the cp is a directory with two subdirectories.
     We actually want the files for either Xcode 3 or Xcode 4 to be copied.
     Using xcodebuild -version, we check for the Xcode version and
     select which of xcode/3/* or xcode/4/* should be the source
     of the copy.

Fixes #5874.

R=golang-dev, minux.ma, adg
CC=golang-dev
https://golang.org/cl/10893044

misc/dist/darwin/scripts/postinstall

@@ -10,9 +10,22 @@ find . -type d -exec chmod ugo+rx \{\} \;
 chmod o-w .
 
 echo "Installing miscellaneous files:"
-XCODE_MISC_DIR="/Library/Application Support/Developer/Shared/Xcode/Specifications/"
-if [ -d "$XCODE_MISC_DIR" ]; then
-	echo "  XCode"
-	cp $GOROOT/misc/xcode/* $XCODE_MISC_DIR
+XCODE_SHARED_DIR="/Library/Application Support/Developer/Shared/Xcode"
+XCODE_MISC_DIR="$XCODE_SHARED_DIR/Specifications/"
+if [ -d "$XCODE_SHARED_DIR" ]; then
+	# Create the XCODE_MISC_DIR if it doesn't exist already
+	mkdir -p "$XCODE_MISC_DIR"
+
+	version=`/usr/bin/xcodebuild -version | sed -n -E 's/^Xcode ([0-9]+)\..*$/\1/p'`
+        
+        # Since command line tools are optional with Xcode 4, a failure of the 
+	# xcodebuild -version command is interpreted as meaning Xcode 4 is the 
+	# version used.
+	if [[ $? -ne 0 ]]; then
+		version=4
+	fi
+
+        echo "  Xcode $version"
+	cp $GOROOT/misc/xcode/$version/* "$XCODE_MISC_DIR"
 fi