Use Content-Type based approach for body matcher

When converting objects to body, dicts and sets order can change
resulting in a different but same body. This fixes the issue by
comparing the enclosed data in the body rather than the body itself
while still allowing raw body matching with the raw_body matcher.

vcr/config.py

@@ -47,6 +47,7 @@ class VCR(object):
             'path': matchers.path,
             'query': matchers.query,
             'headers': matchers.headers,
+            'raw_body': matchers.raw_body,
             'body': matchers.body,
         }
         self.record_mode = record_mode