ca-bundle: install a generated ca-cert bundle for curl

On OSX git calls curl from hashstack, it will fail on https based
repositories if SSL verification is left to the default value of
true.

This commit pulls in a generated ca cert bundle generated from with
the mk-ca-bundle.pl that ships with curl.

It is probably better to ship a semi-regularly updated ca-bundle
than to tell users to turn off verification that verification of
ssl based services are broken.

Signed-off-by: Jimmy Tang <jcftang@gmail.com>
curl: make ca-bundle optional
golang: Add example which uses curl + ca-bundle

git/mercurial complains about not being able to verify ssl certs. This
example demonstrates how to squash this error with the shipped ca
cert bundle.
ca-bundle/curl: be clearer with why you would want ca-bundle
curl: use keyword parameter to enable ca-bundle
curl: remove un-needed parameter
curl: note that curl does not use a CRL out of the box in our case.
Merge pull request #579 from jcftang/wip-ca-bundle

ca-bundle: install a generated ca-cert bundle for curl