Tests in the 'corpus' and 'mapping' folders and the top-level 'corpus'
directory are copied verbatim from the BSON distribution on CPAN.  Because
they invoke BSON.pm for encoding and decoding, they will pick up BSON::XS
and use it for tests.

The t/lib/CleanEnv.pm module in the *BSON* distribution blocks BSON::XS.
The t/lib/CleanEnv.pm module in *this* distribution blocks BSON::PP.  This
way, we can use the same set of tests for both distributions, ensuring
backend compatibility.
