Handle when formula are deleted from taps

The symlinks in Formula must be updated.

Library/Homebrew/cmd/update.rb

@@ -1,4 +1,5 @@
 require 'cmd/tap'
+require 'cmd/untap'
 
 module Homebrew extend self
 
@@ -26,6 +27,9 @@ module Homebrew extend self
         end
       end
     end
+
+    # we unlink first in case the formula has moved to another tap
+    Homebrew.unlink_tap_formula(report.removed_tapped_formula)
     Homebrew.link_tap_formula(report.new_tapped_formula)
 
     if report.empty?
@@ -121,19 +125,27 @@ class Report < Hash
 #    dump_deleted_commands
   end
 
-  def new_tapped_formula
-    fetch(:A, []).map do |path|
-      case path when %r{^Library/Taps(/\w+-\w+/.*)}
+  def tapped_formula_for key
+    fetch(key, []).map do |path|
+      case path when %r{^Library/Taps/(\w+-\w+/.*)}
         Pathname.new($1)
       end
     end.compact
   end
 
+  def new_tapped_formula
+    tapped_formula_for :A
+  end
+
+  def removed_tapped_formula
+    tapped_formula_for :D
+  end
+
   def select_formula key
     fetch(key, []).map do |path|
       case path when %r{^Library/Formula}
         File.basename(path, ".rb")
-      when %r{^Library/Taps/(\w+)-(\w+)/(.*)}
+      when %r{^Library/Taps/(\w+)-(\w+)/(.*)\.rb}
         "#$1/#$2/#{File.basename(path, '.rb')}"
       end
     end.compact.sort