Recognize and extract xar files

Library/Homebrew/download_strategy.rb

@@ -172,9 +172,8 @@ class CurlDownloadStrategy < AbstractDownloadStrategy
     when :lzip
       with_system_path { safe_system "#{lzippath} -dc \"#{tarball_path}\" | tar xf -" }
       chdir
-    when :pkg
-      safe_system '/usr/sbin/pkgutil', '--expand', tarball_path, basename_without_params
-      chdir
+    when :xar
+      safe_system "/usr/bin/xar", "-xf", tarball_path
     when :rar
       quiet_safe_system 'unrar', 'x', {:quiet_flag => '-inul'}, tarball_path
     when :p7zip

Library/Homebrew/extend/pathname.rb

@@ -206,9 +206,6 @@ class Pathname
     when ".jar", ".war"
       # Don't treat jars or wars as compressed
       return
-    when ".pkg"
-      # OS X installer package
-      return :pkg
     when ".gz"
       # If the filename ends with .gz not preceded by .tar
       # then we want to gunzip but not tar
@@ -230,6 +227,7 @@ class Pathname
     when /^LZIP/n               then :lzip
     when /^Rar!/n               then :rar
     when /^7z\xBC\xAF\x27\x1C/n then :p7zip
+    when /^xar!/n               then :xar
     else
       # This code so that bad-tarballs and zips produce good error messages
       # when they don't unarchive properly.