387681 - Fix errors in mapping AD tombstones
    
    The AD tombstone mapping code is not behaving correctly if a
    cn contains a comma (such as a "last, first" type value).  The
    code is supposed to locate the first ":" in the tombstone DN,
    then scan for the first "," after that.  Everything between is
    the GUID.  The problem is that the code is starting at the
    beginning of the string when searching for the "," instead of
    starting at the ":" that was previously found.  This causes the
    "," in the cn to be found instead, which makes us fail to find
    the GUID.
    
    The fix is to simply start searching for the "," from the ":"
    in the tombstone DN.