install, update: AlreadyTappedError never raised.

Library/Homebrew/cmd/install.rb

@@ -31,10 +31,7 @@ module Homebrew extend self
       end
       if not File.exist? name and name =~ HOMEBREW_TAP_FORMULA_REGEX then
         require 'cmd/tap'
-        begin
-          install_tap $1, $2
-        rescue AlreadyTappedError
-        end
+        install_tap $1, $2
       end
     end unless ARGV.force?
 

Library/Homebrew/cmd/update.rb

@@ -61,10 +61,7 @@ module Homebrew extend self
       migration = TAP_MIGRATIONS[f]
       next unless migration
       tap_user, tap_repo = migration.split '/'
-      begin
-        install_tap tap_user, tap_repo
-      rescue AlreadyTappedError
-      end
+      install_tap tap_user, tap_repo
     end if load_tap_migrations
 
     if report.empty?