revocation: OCSP and/or CRL fetching can be disabled

conf/Makefile.am

@@ -80,6 +80,7 @@ plugins = \
 	plugins/radattr.opt \
 	plugins/random.opt \
 	plugins/resolve.opt \
+	plugins/revocation.opt \
 	plugins/socket-default.opt \
 	plugins/sql.opt \
 	plugins/stroke.opt \

conf/plugins/revocation.opt

@@ -0,0 +1,7 @@
+charon.plugins.revocation.enable_ocsp = yes
+	Whether OCSP fetching should be enabled.
+
+charon.plugins.revocation.enable_crl = yes
+        Whether CRL fetching should be enabled.
+
+