Show code references in inherited localization files

[pavelevap]

For example string "Invalid post type" is used several times - on frontend and also in admin. But this string is only in frontend localization file, because this file is also loaded on admin side. That is correct, no need to duplicate strings in different files. But translators do not see code references related to admin file and it can leads to context problems during translation.

It could be very helpfull to modify makepot.php to add related code references to generated .pot files.

Related example: #20809

I am not sure exactly how we'd do this, but I imagine it is possible in some way.

For those interested, makepot's code is here: ​http://i18n.svn.wordpress.org/tools/trunk/