Handle $EDITOR with spaces

Fixes Homebrew/homebrew#40

Library/Homebrew/utils.rb

@@ -91,5 +91,8 @@ def exec_editor *args
       editor='vim'
     end
   end
-  exec editor, *args
+  # we split the editor because especially on mac "mate -w" is common
+  # but we still want to use the comma-delimited version of exec because then
+  # we don't have to escape args, and escaping 100% is tricky
+  exec *(editor.split+args)
 end