Exclude "HEAD" formula from outdated list.

Library/Homebrew/brew.h.rb

@@ -387,7 +387,12 @@ def outdated_brews
 
   results = []
   HOMEBREW_CELLAR.subdirs.each do |keg|
+    # Skip kegs with no versions installed
     next unless keg.subdirs
+
+    # Skip HEAD formulae, consider them "evergreen"
+    next if keg.subdirs.collect{|p|p.basename.to_s}.include? "HEAD"
+
     name = keg.basename.to_s
     if (not (f = Formula.factory(name)).installed? rescue nil)
       results << [keg, name, f.version]