Revision 1294928

AVRO-1031. C: avro_value_cmp doesn't necessarily return {-1,0,1}.

The avro_value_cmp function uses memcmp under the covers (at least for
comparing bytes values), and so it doesn't necessarily return only -1,
0, and 1 as results.  Rather, any negative value can be used for the
less-than case, and any positive value for the greater-than case.  This
patch updates our unit tests to not assume too much about the return
value.