Add full support for Boto

Before this change, vcrpy would not work with modules of Boto (e.g., boto.iam)
that use Boto's CertValidatingHTTPSConnection to connect to AWS (unless you
went through the extra effort of disabling certificate validation during the
tests).  This change adds support for those modules.

vcr/stubs/boto_stubs.py

@@ -0,0 +1,8 @@
+'''Stubs for boto'''
+
+from boto.https_connection import CertValidatingHTTPSConnection
+from ..stubs import VCRHTTPSConnection
+
+
+class VCRCertValidatingHTTPSConnection(VCRHTTPSConnection):
+    _baseclass = CertValidatingHTTPSConnection