Show references without links when there is no source file URL

[dimadin]

Some projects are not public so we can't have links that point to source file. In those cases, we can only show file name and line without link since it could provide some context to translator.

Current example of usage is with translations of wpcom and gravatar. Although whole source of wpcom is not public, most parts of it (WP, bbPress, themes, plugins) are, so translators could see where string is used and see source file via detour. On gravatar, file names are descriptive and sometimes match URL structure so translator could guess where to find string in usage.

To add this functionality, function references in gp-template/helper-functions.php needs to be edited.

I have to patches for this. Difference between this is that they have different hooks. I made one then I thought about better solution.

Since some project can be proprietary so admins might not want to reveal file names, I added hook to override it.

A hook is nice, but not necessary, as this information would be publicly shown in the PO file anyway.

(In [724]) Show references without links when there is no source file URL. props dimadin. fixes #92.