In places where a second rule definition might replace, append to, or
replace items from a base rule, ensure that the source of the second
rule definiton matches the first.
This already existed for defines, but for other changes. There was a
bug where a second definition might exist for a different source, but
the additional rule was used anyway.
This now returns the same error for these other changes e.g. "Rule has
been re-defined..." as define.
Signed-off-by: Mark Stemm <mark.stemm@gmail.com>
