x509: CRL: add tests for non-critical extension

The 'critical' boolean can be set to false in two ways:
- by leaving it implicit (test data generated by openssl)
- by explicitly setting it to false (generated by hand)

tests/data_files/test-ca.opensslconf

@@ -18,5 +18,8 @@ database = /dev/null
 [crl_ext_idp]
 issuingDistributionPoint=critical, @idpdata
 
+[crl_ext_idp_nc]
+issuingDistributionPoint=@idpdata
+
 [idpdata]
 fullname=URI:http://pki.example.com/