Cleanup to r84610 per CR: changed BeforeParserMakeImageLinkObj hook to use a RepoGrou...

Cleanup to r84610 per CR: changed BeforeParserMakeImageLinkObj hook to use a RepoGroup style param array that also excepts a 'broken' parameter. This new parameter replaces the odd "use timestamp '0' to make a broken thumbnail' convention. No other callers are using this hook other  than FR, so the old time/sha1 params where removed.