Fix brew doctor warnings and spurious newline.

Fixes the problems discussed in 34c970 to ensure that `brew doctor`
does not look like it is broken on user setup problems but still
returns a sensible exit code for e.g. BrewBot.

Library/Homebrew/cmd/doctor.rb

@@ -936,9 +936,9 @@ module Homebrew extend self
     checks.methods.select{ |method| method =~ /^check_/ }.sort.each do |method|
       out = checks.send(method)
       unless out.nil? or out.empty?
-        puts unless Homebrew.failed?
         lines = out.to_s.split('\n')
-        ofail lines.shift
+        opoo lines.shift
+        Homebrew.failed = true
         puts lines
       end
     end