cmd/install: use migration_needed?

Closes #411.

Signed-off-by: Xu Cheng <xucheng@me.com>

Library/Homebrew/cmd/install.rb

@@ -132,8 +132,7 @@ module Homebrew
           msg = "#{f.full_name}-#{f.installed_version} already installed"
           msg << ", it's just not linked" unless f.linked_keg.symlink? || f.keg_only?
           opoo msg
-        elsif f.oldname && (dir = HOMEBREW_CELLAR/f.oldname).directory? && !dir.subdirs.empty? \
-            && f.tap == Tab.for_keg(dir.subdirs.first).tap && !ARGV.force?
+        elsif f.migration_needed? && !ARGV.force?
           # Check if the formula we try to install is the same as installed
           # but not migrated one. If --force passed then install anyway.
           opoo "#{f.oldname} already installed, it's just not migrated"