xcode: add new package ID for Mavericks (again).

Closes Homebrew/homebrew#30296.

Library/Homebrew/os/mac/xcode.rb

@@ -147,6 +147,8 @@ module OS
       STANDALONE_PKG_ID = "com.apple.pkg.DeveloperToolsCLILeo"
       FROM_XCODE_PKG_ID = "com.apple.pkg.DeveloperToolsCLI"
       MAVERICKS_PKG_ID = "com.apple.pkg.CLTools_Executables"
+      # Used for Yosemite and Mavericks CLT since June 2014.
+      MAVERICKS_NEW_PKG_ID = "com.apple.pkg.CLTools_Base"
       MAVERICKS_PKG_PATH = "/Library/Developer/CommandLineTools"
 
       # Returns true even if outdated tools are installed, e.g.
@@ -181,7 +183,7 @@ module OS
       end
 
       def detect_version
-        [MAVERICKS_PKG_ID, STANDALONE_PKG_ID, FROM_XCODE_PKG_ID].find do |id|
+        [MAVERICKS_NEW_PKG_ID, MAVERICKS_PKG_ID, STANDALONE_PKG_ID, FROM_XCODE_PKG_ID].find do |id|
           version = MacOS.pkgutil_info(id)[/version: (.+)$/, 1]
           return version if version
         end